What are you doing for white balance? You could experiment with custom settings, or you could put a gray or white card in the frame and balance using that if you shoot RAW.
If that doesn't help you could also evaluate your exposure, as the dark sky could cause you to overexpose the stars, which then could produce "fringing" at the high contrast edges. Look at the discolored stars at 100% or more magnification and see if the centers are blown out and the edges ringed by red, etc.