I made a cake and the frosting was a very dark blue. I used mostly Americolor gel and then a little CK powder food coloring (ran out of the Americolor).
It turned a lot of people's teeth green. Is there any way to prevent this? Other than not deeply coloring frosting? The frosting was just a standard American Buttercream (butter, heavy cream, powdered sugar).
I would hate to think I can only make light colored frosting.
I don't think there's much of a way to prevent it since teeth are porous. This is why I advise brides to have a light flavor and light frosting for the cutting cake - - can't have blue teeth in the pictures!
My grandkids love it when I make them a cake with a black fondant ball border. It freaks their mother out when their poop turns bright blue.
Make the icing early. Colors will deepen as it sits, so if you make it earlier, you will use less coloring.
For all over color, maybe consider getting an airbrush.