change how modal num works so that it is only clipped to 255 if setting a new colour/alpha value

fcore/normal-mode.sml

@@ -247,14 +247,8 @@ struct
         (model, drawMsg)
       end
 
-  fun updateNum (model: app_type, inputNum) =
-    let
-      val oldNum = #modalNum model
-      val newNum = oldNum * 10 + inputNum
-      val newNum = if newNum > 255 then 0 else newNum
-    in
+  fun updateNum (model: app_type, newNum) =
       (AppWith.modalNum (model, newNum), [])
-    end
 
   fun updateRed model = (AppWith.r model, [])
   fun updateGreen model = (AppWith.g model, [])