add functionality to draw in different colours

fcore/app-init.sml

@@ -24,7 +24,7 @@ struct
 
       val maxPoints = Int.max (canvasWidth, canvasHeight)
       val squares = Vector.tabulate (maxPoints, fn _ =>
-        Vector.tabulate (maxPoints, fn _ => 0))
+        Vector.tabulate (maxPoints, fn _ => {r = 0, g = 0, b = 0, a = 0}))
     in
       { mode = AppType.NORMAL_MODE
       , squares = squares
@@ -43,10 +43,10 @@ struct
       , openFilePath = ""
       , fileBrowser = Vector.fromList []
       , fileBrowserIdx = 0
-      , r = 0.0
-      , g = 0.0
-      , b = 0.0
-      , a = 1.0
+      , r = 0
+      , g = 0
+      , b = 0
+      , a = 1
       , modalNum = 0
       }
     end