Yes, you can paint casement windows. However, the process will depend on the window material. For wood casement windows, you must lightly sand the surface, apply a primer and then paint.
For aluminium casement windows, special preparation and paints are needed for the paint to adhere correctly.
Always protect the window’s operational mechanisms from paint to keep them functioning smoothly. Lastly, remember that painting might void your window’s warranty, so it’s best to check this beforehand.