After every use.

Get yourself a green corrector from L.A.Girl and use it under your current foundation on areas where you have redness.

Try vaseline or some mineral oil - they have the same properties. Is it stain or you can remove actual paint? Refer to the package on how to remove it. Some paints need special removers, depends on what they are based on. If this is a stain left after paint removal, you need to be patient, your skin will exfoliate and go back to normal. Be gentle!