I was at Giant Eagle (a large grocery chain) a few weeks ago with a friend. At about the same time we spotted this cake and had pretty much the same reaction: "Hey, look, it's a bi cake, haha. We should take a picture." There were several of 'em in these colors. I thought about buying one, but they were $5.99, and it was only half a cake.
The sprinkles on the top of the cake are, appropriately, rainbow.