Do the normal erase challenge thing. then on a different frame put a color around the erased part that you think that would go with the drawing. then use the paintroller tool and (you can use any size) use the darkest grey (the one I use before I started using black) and then just go all crazy and spread it on the colour. Then go to the first frame with your (hopefully original XP jk) art and copy that frame. Then go to the second frame with the color and paste it.

k!