wow, the only problem I have telling a newbie to use cheap craft paint is, that depending on the air brush quality, spraying the cheaper paints can be a challenge due to the size of the pigment particles and pearling in the paints. But to the point about learning, it is a way to learn brush control.

I would be more inclined to say buy better paints such as Createx, Auto Air and a few others that are paints designed for air brushs and just buy a sufficient amount of white and black to learn with.

Regardless experiment with what ever paint you use, varying air pressure and how thin/thick the paint is. And remember there are no mistakes, only happy errors.