Hard polyurethanes can be painted but the surface to be painted must first be correctly prepared. If you want to paint components no silicone-containing release agent should be used in the production. Silicone-based release agents are difficult to remove from the surface of your polyurethane and thus prevent adhesion of the paint on the component.
Before painting the surface should be slightly roughened (for example with sandpaper) and cleaned with e.g. silicone remover.