Grantanow is quite right; red pigment in paint fades much quicker than any other, they're sensitive to light, heat, and oxygen, which can cause the pigment to break down and discolour. Red pigments absorb more light than other colours. Red cars, red doors and red fabrics fade much quicker, especially if exposed to bright sunlight. If your door is south facing, the problem is exacerbated. Respraying is an option.
What sort of family would you not want to marry into?
