UI|Client|Default Style: Use accent color in default dialog button(s)

It helps to have a subtle color hint to show which button is the
default/recommended one.

Also cleaned up colors.dei a little.

doomsday/client/data/defaultstyle.pack/colors.dei

@@ -2,17 +2,27 @@
 
 script { import gui, Version }
 
-color text       { rgb <1.0, 1.0, 1.0> }
-color background { rgb <0.0, 0.0, 0.0, 0.75> }
-color accent     { rgb <1.0, 0.8, 0.4> }
-color glow       { rgb <1.0, 1.0, 1.0, 0.14> }
+#
+# THE BASIC COLOR PALETTE
+#
+
+color text        { rgb <1.0, 1.0, 1.0> }
+color background  { rgb <0.0, 0.0, 0.0, 0.75> }
+color accent      { rgb <1.0, 0.8, 0.4> }
+color glow        { rgb <1.0, 1.0, 1.0, 0.14> }
+
+color textaccent  { rgb $= gui.colorMix(text.rgb, accent.rgb, 0.5) }
 
 group inverted {
     color text       { rgb <0.0, 0.0, 0.0> }
     color background { rgb <1.0, 1.0, 1.0, 0.75> }
     color glow       { rgb <0.0, 0.0, 0.0, 0.15> }
 }
 
+#
+# COLORS FOR SPECIFIC WIDGETS
+#
+
 group label {
     color highlight { rgb <1.0, 1.0, 1.0> }
     color dimmed    { rgb <0.72, 0.72, 0.68> }
@@ -37,11 +47,12 @@ group progress {
 
 group dialog {
     color background { rgb $= gui.colorAlpha(background.rgb, 0.9) }
+    color default    { rgb $= textaccent.rgb }
 }
 
 group editor {
     color cursor { rgb $= gui.colorAlpha(accent.rgb, 0.7) }
-    color hint   { rgb $= gui.colorMix(text.rgb, accent.rgb, 0.5) }
+    color hint   { rgb $= textaccent.rgb }
 
     group completion {
         color background { rgb <1.0, 1.0, 1.0> }

doomsday/client/src/ui/widgets/dialogwidget.cpp

@@ -215,10 +215,16 @@ DENG2_OBSERVES(ui::Context, Removal)
                 }
             }
 
+            // Highlight the default button(s).
             if(i->role().testFlag(Default))
             {
+                but.setTextColor("dialog.default");
                 but.setText(_E(b) + but.text());
             }
+            else
+            {
+                but.setTextColor("text");
+            }
         }
     }