It seems that everytime I try to color MMF a dark color like black or royal blue it seems to break and crack and fall apart when I try to cover a cake. Am I doing something wrong?
Probably not - fondant has a hard time when you are trying to get it to a really dark color. It gets overworked.
The only thing that I can suggest is to add the color when you are mixing it in the KA. That way it won't get overworked. Hope this helps.