The paint box you had as a kid, on iPhone Duo. Open the phone like a little laptop. The bottom half is a white plastic paint box with eight oval watercolor cakes, a water cup and two mixing wells. The top half is the paper. Close the phone and your painting is saved. It's real watercolor, or as close as a phone gets: • Dry cakes turn glossy when you rub them with a wet brush • Paint bleeds into wet paper and dries with darker edges • Colors mix like paint: yellow over blue goes green • Skip…