I've had this happen a few times to me when the icing was in the container, but never ona cake until recently. I'm retaking the wilton courses with a friend and it happened on that blue rainbow cake. My blue had specs. I also had a container of violet practice icing where the colors seperated (you could see blue and reddish colors). I don't think there's anything you can do once it's on the cake, but with my practice icing I remixed it and it stayed fine for three more weeks (in and out of the fridge for the courses). I think the trick is to make sure your color is mixed really well. Last year when I started cake decorating and took the classes i never had this problem and my colors were all new. Well, I have all the same colors and they are thicker and some are clumpy, so it could easily be old color. I'm saving up to make an americolor order LOL.