Practice! Once you start seeing warm and cool colors you can continue to learn! Go easy on yourself in the beginning, sometimes it takes a while. There will be a moment when you 'get it' - after this you must still practice the visual concept to hone your skill. Often students will say they think they get it only to have it slip away, keep practicing... this is when you know you are close to keeping this special way of seeing for good. You are un-learning what your brain is telling you (but it's only a white cup, there is no color). With practice you will see more and more color in shadows and light.