As far as I know, all colored objects fade on exposure to UV radiation or even sun light. UV radiation with its short wavelength can excite the dye molecule which leads to breaking of its chemical bonds or producing free radicals that oxidize the dye, acting like bleach.These processes will cause degradation of the dye, destroying its chromophor and the color is gradually faded. Ultraviolet (UV) light from the sun accounts for approximately 40% of the fading process. Visible light and solar heat each contribute approximately 25% and 10% can be attributed to miscellaneous effects such as indoor artificial lighting, humidity, gassing, heat and poor dye affinity. Addition of some materials, such as TiO2, can have a protection effect on paints because of UV absorption.