A simple request which will help when creating overlays for animated sprites.

I notice that the error message that comes up when you set a palette color to an already used/existing color is gone.. when was that done?

So when I'm creating overlays for sprites, I draw clothes and whatnot over the character in all the states and animations. Then I make all the colors of the base sprite(mob) one color like pure white. Then I have to enter every frame of every state and swap the white to transparent. I was wondering if you could add a feature to where you could set a color palette to null or complete transparent and it would effected all the frames and icon_states?