Ensure color mixer works in New dialog

and sync README docs to capture that it, and rainbow palette,
may be used.

docs/CHANGES.txt

@@ -7,7 +7,7 @@ Various contributors (see below, and AUTHORS.txt)
 http://www.tuxpaint.org/
 
 
-2022.February.22 (0.9.28)
+2022.February.23 (0.9.28)
   * Improvements to "Paint" and "Lines" tools:
     ------------------------------------------
     * Brush spacing may now be altered within Tux Paint.

docs/en/README.txt

@@ -7,7 +7,7 @@
                              https://tuxpaint.org/
                            @TuxPaintTweets on Twitter
 
-                               February 21, 2022
+                               February 23, 2022
 
      ----------------------------------------------------------------------
 
@@ -616,6 +616,15 @@ Available Tools
                  Note: You can also press [Control / ⌘] + [N] on the keyboard
                  to start a new drawing.
 
+                 Special Solid Background Color Choices
+
+                   Along with the preset solid colors, you can also choose
+                   colors using a rainbow palette or a "color mixer". These
+                   operate identically to the options found in the color
+                   palette shown below the canvas when drawing a picture. See
+                   Main Screen > Lower: Colors > Special color options for
+                   details.
+
                  'Starter' & Template Images
 
                    'Starters' can behave like a page from a coloring book — a

docs/en/html/README.html

@@ -29,7 +29,7 @@
       </p>
 
       <p>
-        February 21, 2022      </p>
+        February 23, 2022      </p>
     </center>
 
     <hr size="2"
@@ -351,7 +351,7 @@
                  "[Colors - Black, White, Red, Pink, Orange, Yellow, Green, Cyan, Blue, Purple, Brown, Grey]">
             </p>
 
-            <p>
+            <p id="special_color_options">
               On the far right are three special color options:              <ul>
                 <li>The "color picker" (which has an outline of an eye-dropper) allows you to pick a color found within your drawing. A shortcut key is available to access this feature quickly; see below.                <li>The rainbow palette allows you to pick a color from within a box containing thousands of colors.</li>
                 <li>The "color mixer" (which has silhouette of a paint palette) allows you to create colors by blending primary additive colors &mdash; red, yellow, and blue &mdash; along with white (to "tint"), grey (to "tone"), and black (to "shade").  The ratios of colors added are shown at the bottom.</li>
@@ -867,6 +867,13 @@
 
               <p>
                 <strong>Note:</strong> You can also press <b><code>[Control / &#8984;]</code></b> + <code><b>[N]</b></code> on the keyboard to start a new drawing.              </p>
+
+              <strong>Special Solid Background Color Choices</strong>
+              <blockquote>
+                <p>
+                  Along with the preset solid colors, you can also choose colors using a rainbow palette or a "color mixer". These operate identically to the options found in the color palette shown below the canvas when drawing a picture. See <a href="#special_color_options">Main Screen &gt; Lower: Colors &gt; Special color options</a> for details.                </p>
+              </blockquote>
+
               <strong>'Starter' &amp; Template Images</strong>
               <blockquote>
                 <p>

docs/es_ES.UTF-8/README.txt

@@ -7,7 +7,7 @@
                              https://tuxpaint.org/
                            @TuxPaintTweets on Twitter
 
-                                febrero 21, 2022
+                                febrero 23, 2022
 
      ----------------------------------------------------------------------
 
@@ -616,6 +616,15 @@ Available Tools
                  Note: You can also press [Control / ⌘] + [N] on the keyboard
                  to start a new drawing.
 
+                 Special Solid Background Color Choices
+
+                   Along with the preset solid colors, you can also choose
+                   colors using a rainbow palette or a "color mixer". These
+                   operate identically to the options found in the color
+                   palette shown below the canvas when drawing a picture. See
+                   Main Screen > Lower: Colors > Special color options for
+                   details.
+
                  'Starter' & Template Images
 
                    'Starters' can behave like a page from a coloring book — a

docs/es_ES.UTF-8/html/README.html

@@ -29,7 +29,7 @@
       </p>
 
       <p>
-        febrero 21, 2022      </p>
+        febrero 23, 2022      </p>
     </center>
 
     <hr size="2"
@@ -351,7 +351,7 @@
                  "[Colors - Black, White, Red, Pink, Orange, Yellow, Green, Cyan, Blue, Purple, Brown, Grey]">
             </p>
 
-            <p>
+            <p id="special_color_options">
               On the far right are three special color options:              <ul>
                 <li>The "color picker" (which has an outline of an eye-dropper) allows you to pick a color found within your drawing. A shortcut key is available to access this feature quickly; see below.                <li>The rainbow palette allows you to pick a color from within a box containing thousands of colors.</li>
                 <li>The "color mixer" (which has silhouette of a paint palette) allows you to create colors by blending primary additive colors &mdash; red, yellow, and blue &mdash; along with white (to "tint"), grey (to "tone"), and black (to "shade").  The ratios of colors added are shown at the bottom.</li>
@@ -867,6 +867,13 @@
 
               <p>
                 <strong>Note:</strong> You can also press <b><code>[Control / &#8984;]</code></b> + <code><b>[N]</b></code> on the keyboard to start a new drawing.              </p>
+
+              <strong>Special Solid Background Color Choices</strong>
+              <blockquote>
+                <p>
+                  Along with the preset solid colors, you can also choose colors using a rainbow palette or a "color mixer". These operate identically to the options found in the color palette shown below the canvas when drawing a picture. See <a href="#special_color_options">Main Screen &gt; Lower: Colors &gt; Special color options</a> for details.                </p>
+              </blockquote>
+
               <strong>'Starter' &amp; Template Images</strong>
               <blockquote>
                 <p>

docs/fr_FR.UTF-8/README.txt

@@ -7,7 +7,7 @@
                              https://tuxpaint.org/
                            @TuxPaintTweets on Twitter
 
-                                février 21, 2022
+                                février 23, 2022
 
      ----------------------------------------------------------------------
 
@@ -656,6 +656,15 @@ Outils disponibles
                  Remarque : vous pouvez également appuyer [Control / ⌘] + [N]
                  sur le clavier pour commencer un nouveau dessin.
 
+                 Special Solid Background Color Choices
+
+                   Along with the preset solid colors, you can also choose
+                   colors using a rainbow palette or a "color mixer". These
+                   operate identically to the options found in the color
+                   palette shown below the canvas when drawing a picture. See
+                   Main Screen > Lower: Colors > Special color options for
+                   details.
+
                  Images de "Démarrage" et images "Modèle"
 
                    Les "Images de démarrage" se comportent comme une page

docs/fr_FR.UTF-8/html/README.html

@@ -29,7 +29,7 @@
       </p>
 
       <p>
-        février 21, 2022      </p>
+        février 23, 2022      </p>
     </center>
 
     <hr size="2"
@@ -351,7 +351,7 @@
                  "[Couleurs - Noir, Blanc, Rouge, Rose, Orange, Jaune, Vert, Cyan, Bleu, Pourpre, Brun, Gris]">
             </p>
 
-            <p>
+            <p id="special_color_options">
               On the far right are three special color options:              <ul>
                 <li>The "color picker" (which has an outline of an eye-dropper) allows you to pick a color found within your drawing. A shortcut key is available to access this feature quickly; see below.                <li>The rainbow palette allows you to pick a color from within a box containing thousands of colors.</li>
                 <li>The "color mixer" (which has silhouette of a paint palette) allows you to create colors by blending primary additive colors &mdash; red, yellow, and blue &mdash; along with white (to "tint"), grey (to "tone"), and black (to "shade").  The ratios of colors added are shown at the bottom.</li>
@@ -867,6 +867,13 @@
 
               <p>
                 <strong>Remarque :</strong> vous pouvez également appuyer <b><code>[Control / &#8984;]</code></b> + <code><b>[N]</b></code> sur le clavier pour commencer un nouveau dessin.              </p>
+
+              <strong>Special Solid Background Color Choices</strong>
+              <blockquote>
+                <p>
+                  Along with the preset solid colors, you can also choose colors using a rainbow palette or a "color mixer". These operate identically to the options found in the color palette shown below the canvas when drawing a picture. See <a href="#special_color_options">Main Screen &gt; Lower: Colors &gt; Special color options</a> for details.                </p>
+              </blockquote>
+
               <strong>Images de "Démarrage" et images "Modèle"</strong>
               <blockquote>
                 <p>

docs/gl_ES.UTF-8/README.txt

@@ -7,7 +7,7 @@
                              https://tuxpaint.org/
                            @TuxPaintTweets on Twitter
 
-                             21 de Febreiro de 2022
+                             23 de Febreiro de 2022
 
      ----------------------------------------------------------------------
 
@@ -630,6 +630,15 @@ Ferramentas dispoñíbeis
                  Nota: Tamén pode premer [Control / ⌘] + [N] no teclado para
                  iniciar un novo debuxo.
 
+                 Special Solid Background Color Choices
+
+                   Along with the preset solid colors, you can also choose
+                   colors using a rainbow palette or a "color mixer". These
+                   operate identically to the options found in the color
+                   palette shown below the canvas when drawing a picture. See
+                   Main Screen > Lower: Colors > Special color options for
+                   details.
+
                  Imaxes «de comezo» e de «modelo»
 
                    As «imaxes de inicio» poden comportarse como unha páxina

docs/gl_ES.UTF-8/html/README.html

@@ -29,7 +29,7 @@
       </p>
 
       <p>
-        21 de Febreiro de 2022      </p>
+        23 de Febreiro de 2022      </p>
     </center>
 
     <hr size="2"
@@ -351,7 +351,7 @@
                  "[Cores: negro, branco, vermello, rosa, laranxa, amarelo, verde, cian, azul, roxo, marrón, gris]">
             </p>
 
-            <p>
+            <p id="special_color_options">
               On the far right are three special color options:              <ul>
                 <li>The "color picker" (which has an outline of an eye-dropper) allows you to pick a color found within your drawing. A shortcut key is available to access this feature quickly; see below.                <li>The rainbow palette allows you to pick a color from within a box containing thousands of colors.</li>
                 <li>The "color mixer" (which has silhouette of a paint palette) allows you to create colors by blending primary additive colors &mdash; red, yellow, and blue &mdash; along with white (to "tint"), grey (to "tone"), and black (to "shade").  The ratios of colors added are shown at the bottom.</li>
@@ -867,6 +867,13 @@
 
               <p>
                 <strong>Nota:</strong> Tamén pode premer <b><code>[Control / &#8984;]</code></b> + <code><b>[N]</b></code> no teclado para iniciar un novo debuxo.              </p>
+
+              <strong>Special Solid Background Color Choices</strong>
+              <blockquote>
+                <p>
+                  Along with the preset solid colors, you can also choose colors using a rainbow palette or a "color mixer". These operate identically to the options found in the color palette shown below the canvas when drawing a picture. See <a href="#special_color_options">Main Screen &gt; Lower: Colors &gt; Special color options</a> for details.                </p>
+              </blockquote>
+
               <strong>Imaxes «de comezo» e de «modelo»</strong>
               <blockquote>
                 <p>

docs/ja_JP.UTF-8/README.txt

@@ -7,7 +7,7 @@
                              https://tuxpaint.org/
                            @TuxPaintTweets on Twitter
 
-                                   2022年2月21日
+                                   2022年2月23日
 
      ----------------------------------------------------------------------
 
@@ -449,6 +449,15 @@ Tux Paint の起動
 
                  注: キーボードで [Control / ⌘] + [N] を押しても新規作成ができます。
 
+                 Special Solid Background Color Choices
+
+                   Along with the preset solid colors, you can also choose
+                   colors using a rainbow palette or a "color mixer". These
+                   operate identically to the options found in the color
+                   palette shown below the canvas when drawing a picture. See
+                   Main Screen > Lower: Colors > Special color options for
+                   details.
+
                  レイヤー画像
 
                    レイヤー画像には、塗り絵のページのようなもの（白黒の線で描かれ、色を塗ることができる）や、前景レイヤーと背景レイヤーに挟まれた部分に絵を描ける３Ｄ画像のようなものがあります。

docs/ja_JP.UTF-8/html/README.html

@@ -29,7 +29,7 @@
       </p>
 
       <p>
-        2022年2月21日      </p>
+        2022年2月23日      </p>
     </center>
 
     <hr size="2"
@@ -351,7 +351,7 @@
                  "[いろ - いろ - くろ、しろ、あか、ぴんく、おれんじ、きいろ、みどり、みずいろ、あお、むらさき、ちゃいろ、はいいろ]">
             </p>
 
-            <p>
+            <p id="special_color_options">
               On the far right are three special color options:              <ul>
                 <li>The "color picker" (which has an outline of an eye-dropper) allows you to pick a color found within your drawing. A shortcut key is available to access this feature quickly; see below.                <li>The rainbow palette allows you to pick a color from within a box containing thousands of colors.</li>
                 <li>The "color mixer" (which has silhouette of a paint palette) allows you to create colors by blending primary additive colors &mdash; red, yellow, and blue &mdash; along with white (to "tint"), grey (to "tone"), and black (to "shade").  The ratios of colors added are shown at the bottom.</li>
@@ -867,6 +867,13 @@
 
               <p>
                 <strong>注:</strong> キーボードで <b><code>[Control / &#8984;]</code></b> + <code><b>[N]</b></code> を押しても新規作成ができます。              </p>
+
+              <strong>Special Solid Background Color Choices</strong>
+              <blockquote>
+                <p>
+                  Along with the preset solid colors, you can also choose colors using a rainbow palette or a "color mixer". These operate identically to the options found in the color palette shown below the canvas when drawing a picture. See <a href="#special_color_options">Main Screen &gt; Lower: Colors &gt; Special color options</a> for details.                </p>
+              </blockquote>
+
               <strong>レイヤー画像</strong>
               <blockquote>
                 <p>

src/tuxpaint.c

@@ -22,7 +22,7 @@
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   (See COPYING.txt)
 
-  June 14, 2002 - February 22, 2022
+  June 14, 2002 - February 23, 2022
 */
 
 #include "platform.h"
@@ -681,9 +681,10 @@ static int NUM_COLORS;
 static Uint8 **color_hexes;
 static char **color_names;
 
-#define COLOR_MIXER (NUM_COLORS - 1) /* Mix colors together */
+/* Special color options (from left-to-right (very last entry)) */
 #define COLOR_SELECTOR (NUM_COLORS - 3) /* Pick a color from the canvas */
 #define COLOR_PICKER (NUM_COLORS - 2) /* Pick a color from a palette */
+#define COLOR_MIXER (NUM_COLORS - 1) /* Mix colors together */
 
 /* Show debugging stuff: */
 
@@ -21292,6 +21293,11 @@ static int do_new_dialog(void)
               if (do_color_picker() == 0)
                 return (0);
             }
+          else if (which == COLOR_MIXER)
+            {
+              if (do_color_mix() == 0)
+                return (0);
+            }
 
           /* FIXME: Don't do anything and go back to Open dialog if they
              hit BACK in color picker! */
@@ -21410,13 +21416,20 @@ static int do_new_dialog_add_colors(SDL_Surface * *thumbs, int num_files, int *d
               *white_in_palette = j;
             }
         }
-      else
+      else if (j == COLOR_PICKER)
         {
           /* Color picker: */
 
           thumbs[num_files] = thumbnail(img_color_picker, THUMB_W - 20, THUMB_H - 20, 0);
           added = 1;
         }
+      else if (j == COLOR_MIXER)
+        {
+          /* Color mixer: */
+
+          thumbs[num_files] = thumbnail(img_color_mix, THUMB_W - 20, THUMB_H - 20, 0);
+          added = 1;
+        }
 
       if (added)
         {