add ability to select cursor colour

fcore/normal-mode.sml

@@ -263,6 +263,16 @@ struct
   fun updateBlue model = (AppWith.b model, [])
   fun updateAlpha model = (AppWith.a model, [])
 
+  fun selectCursorColour (model: app_type) =
+    let
+      val {squares, arrowX, arrowY, ...} = model
+      val yAxis = Vector.sub (squares, arrowX)
+      val {r, g, b, a} = Vector.sub (yAxis, arrowY)
+      val model = AppWith.cursorColour (model, r, g, b, a)
+    in
+      (model, [])
+    end
+
   fun updateCanvas (model, canvasWidth, canvasHeight) =
     let
       val
@@ -359,6 +369,7 @@ struct
     | KEY_G => updateGreen model
     | KEY_B => updateBlue model
     | KEY_A => updateAlpha model
+    | KEY_C => selectCursorColour model
     | KEY_W => updateCanvasWidth model
     | KEY_H => updateCanvasHeight model
     | KEY_M => enterMoveMode model