To answer a previous question, yes, you can paint leather. There are specific paints (usually sprays) specifically meant to paint leather. You can also paint leather with acrylic craft paint, which stays somewhat flexible when dry.
I scratchbuilt these seats for my Pocher RR... they have real foam padding and are upholstered not with real leather, but a synthetic "leather" material that looks exactly like the real thing. I used acrylic gray craft paint on it, and even when you press down the seat cushions, the paint doesn't flake or crack. I don't see why a paint like this wouldn't also work the same way on real leather.