Basic science.
Red paint absorbs yellow through blue light and reflects the red only.
Red light has the least energy and blue the most energy, beyond blue is ultra violet, X rays then gamma rays with more and more energy.
The energy from the absorbed blue light has to go somewhere, it mostly becomes heat but some breaks chemical bonds in the pigment which shows as fading.
So blue paint reflects the energetic light and is fade resistant. Most red pigments fade in sunlight UV blocking polishes help but are not perfect.