This time around I decided to try Bitch, PhD’s suggestion of using colored sugars or rainbow sprinkles anchored in the horses with butter. (I had thought about using colored sugar, etc., but couldn’t figure out how to make it stay in the horses I might be able to do complex integrals, but anchoring sugar in a cake pan with butter is just too hard to figure out on my own.)
I tried lots of different sprinkles to see what would turn out best several colors of sugar, rainbow jimmies, rainbow nonpareils, rainbow sequins. After loading up the horses, I put the pan in the freezer for a few minutes while mixing up the batter. This kept the sprinkles in place when I put the batter in the pan.
I’m not sure it turned out better than the colored batter attempt:
The jimmies, nonopareils, and sequins all ended up melting into the cake, though they did still keep their colors basically in the shape of their respective horses. The sugars seemed to slop all over, despite my best efforts to clean up the pan before adding the batter. The purple actually looks pretty good, and the blue and purple show up much better than the pink and green. Hmm…I didn’t have any of the crystal-type decorative sugars…I wonder if those would have worked better. I have one other idea to try, too; though, I’m beginning to think I might be stuck frosing the horses after baking.