I used the TARDIS silicon molds from ThinkGeek and... they were awful. I think basic cake is too 'spongy' since absolutely zero details showed up.
Since I have to go the grocery store again tomorrow (freaking forgotten canned tomatoes) I shall try again with a blonde brownie mix that I'll dye blue. The new theory is that a denser batter would show the the TARDIS pattern.
Either that or I burn the house down due to frustration.