First do white balancing. The best approach is to have the camera do it, then you can post process it to improve it if you have some reference white in the field of view. Be sure to do a flat field correction first to compensate for shading of the lens and camera.
After that you can do contrast enhancement. But you have to define exactly what that means because there might be different ways of doing it depending on how you want to affect the color gamut.
