Yeah, the bleeding above is an example of not enough dry time between colors, or icings that are too loose and taking too long to dry.
It's really tough to diagnose issues w/o seeing exactly what you've done, but here are some other suggestions:
It's best not to leave fresh egg whites too long at room temp, but I do think your icing is picking up moisture from the fridge. Maybe you need to try a dehydrator or fan to quick-dry your icings, or use meringue powder or pasteurized whites as a base for your icing so it can be left unrefrigerated?
Another IMPORTANT thing to consider is the thickness of your icing when you apply it. I try to push my icings to the thickest consistency possible for a given task, because the thicker the icing is, the quicker it dries - and the less time it has to bleed or mottle on you. Perhaps your icing was thinner/looser than it needed to be?
I don't work with Americolor, so I can't speak to how colorfast those colorings are. I work with Chefmaster, and though I have on occasion seen a small amount of mottling (mostly when humid out), I have never seen this much. If AFTER trying a thicker icing, not refrigerating it and quick-drying it, you still have this trouble, then I would suggest trying another brand. But many, many people use Americolor with success, so I think it's an issue of either too loose/wet icing or ambient conditions messing with you.