If you don’t like yellow or white cake, you can use any of the cake mix flavors on the market. As mentioned, a brownie or muffin mix would also be good for consistency. In fact, since you are just using the dry mix, you could use pound cake, bundt cake, or sponge cake. As long as you don't use the ingredients listed on the back of the box, it will not change the texture of this dessert much.