I am making a cake for my godson's birthday this week. He passed away a few years ago and my friend asked me to make a cake to share with our co-workers and and kids at school. I would like to make a rainbow coming out of the sky...but I don't want a blaring red,yellow, orange, etc. rainbow. I would like to make it look very delicate looking (like a real rainbow would look). Are there any cool techniques out there for buttercream frosting that I could try to get a cool...