I made a birthday cake for a friend this weekend. She requested that the icing be purple. When i got up this morning after the icing had "crusted", there were tiny blue looking polka dots all over the cake. Does anyone have a clue as to what might have caused this??

It could be a few things:

1. Maybe the color wasn't mixed in well enough--that happened to me once. I made a pink frosting and it looked fine when I put it on, but had dark red dots in it the next morning.

2. Maybe your colors are getting old and are starting to separate.

3. Maybe the salt wasn't completely dissolved in your buttercream. Usually when this happens to me, the polka dot is a lighter color than the frosting---lavendar dots in purple icing, light blue dots in dark blue icing, etc. To prevent this, I now dissolve the salt in the water that I need for the icing, and then add the mixture to the rest of the ingredients. I haven't had dots like these since I started dissolving the salt first.

Hope this helps!