I'm sure some of you already know this. Go to a food store and buy food dyes. I bought a set of 4 different colors for like $4 at Giant, and that'll last a lifetime Fill up you airbrush with water, put 1-3 drops of a dye and practice airbrushing on a piece of paper. Obviously, food dyes are not harmful to our body. Cleaning couldn't be easier; just shoot some water after you're done. No disassembly is needed.
All I can say is my ability to detail-airbrush has greatly improved since I got to know this trick a few days ago. Your mileage may vary, of course.