I made these around Christmas, so I tried using the powder food coloring to make the frosting (and thus, the insides) of the cake truffles red and green. I got a pink and a green-ish. Not too bad, but not what I was going for either.
For these, I baked up a rectangular Lady Cake from Joy of Cooking, broke it in half, and crumbled each half into a differently colored bowl of frosting. I use 1/4 cup of shortening to every two cups of powdered sugar, about 1/4 tsp of vanilla and 1/4 tsp of almond, and enough milk to make it whatever consistency I'm going for. I used a bit much milk this time, because I added the milk to the flavorings and added as much food coloring powder as I could, trying to color the frosting. The cake truffles turned out well anyway. Once the innards (cake and frosting) were fully mixed, I rolled them into small balls, put them on wax paper, and put them in the fridge to solidify a bit. I tried to dip some before giving them enough time to solidify, and that didn't work. Make sure your truffle innards are solid before dipping!
I dipped half of each color in dark chocolate and the other half in white chocolate. The white chocolate was somewhat uncooperative using the double boiler method, but works quite well in the microwave. Mmmmm, delicious! I also added some silver dragees to some, but not everyone was interested in those. Surprising how many people are terrified of the little silver balls. I know, I know, the state of California has found them to be carcinogenic, but the quantity you'd have to eat to cause problems is a lot more than you'll ever have! Anyway, they were great and everyone liked them. I've also made some using the Quick Cocoa Cake from Joy of Cooking and either my favorite frosting or chocolate ganache for some really, really chocolatey truffles. Both are excellent, though my frosting mixed with the cake tastes exactly like Count Chocula cereal. Interesting find.