core: config: Add configuration options for keyboard colors

[richard: prefix commit message with code modified and sign]

README.md

@@ -122,6 +122,15 @@ Configuration example:
       height: 185
       input-method: true
 
+    colors:
+      background: [0, 0, 0]
+      keycap: [0, 0, 0]
+      keycap_pressed: [51,51,51]
+      label: [255, 255, 255]
+      label_locked: [25, 255, 0]
+      label_pressed: [255, 153, 0]
+      sublabel: [178, 178, 178]
+
 # License
 
 Unfettered Keyboard is free software; you can redistribute it and/or modify