Wow! So many directions this can go! I use liquid egg whites and powdered sugar only. I think the more ingredients in your icing the more problems you'll have. My icing has never cracked, fallen off, bubbled, etc. It does crater when it dries sometimes but that's because I don't use a fan or dehydrator. The only times I have problems with coloring has been when I mix paste and gel colors. Again, I think the more ingredients that are being mixed the more potential problems. It'll be interesting to see what others say.
I agree with all of this.