Good question! There is no real color count, but I do prefer that you don't use any more than 15 or 16 colors for this week. I'll add that to the OP :o Otherwise there is no actual max color count, I just like to see color efficiency. Try not to waste your colors; try to get rid of any of them that are redundant. Preferably ones that are so close to another color that you would get the same result if you were to have merged them together as one color

And by pixel limit, I mean you cannot change anything outside of the silhouette. Think of the silhouette as your only canvas: you cannot go a single pixel past the borders of the silhouette. if that makes a little more sense? ^^