Painting your Rex
More details to come.
The short version is that I recommend using Jacquard brand fabric paints, especially the Neopaque line. Those have a higher concentration of pigment, so the quantity of paint covers more area and needs fewer coats. Depending on the color, I find two to three coats sufficient, and in some cases only one coat will do!
Regardless of brand, fabric paint will be beneficial, because it's made to be flexible, so it's less likely to crack and flake off as you move or inflate and deflate the suit. You can get cheap acrylic paint and mix it with a fabric medium to add flexibility, but it will also dilute the paint, so you'll need more coats.
Always paint your suit while fully inflated. Use elastic bands to close the wrist and ankle holes, turn the fans on, and zip it up empty. No model needed! Do not deflate until the paint is completely dry (no longer tacky to the touch).
For the most part, the paint will survive wear and tear and the suit being deflated and packed up for extended periods of time. However, you may find small touch-ups are needed the next time you wear the suit, usually around the arm and leg seams.