If the whole bumper has changed color evenly, it seems that the bumper material is reacting with the rubber/undercoating from the bumper or most likely, after 15 years, prolly some of it in the sun, parked outside, the bumper/side skirts have reacted to the uv rays differently than the paint.
I mean, what if your whole car changed color just like this bumper--red fading to pink---that would be kinda odd! no?
I've seen this on several older cars. Maybe it was defective bumper material or something. mmmm....maybe call the dealer and ask them if they've run into this before, what the problem is and what they do about it? Paint will eventually come off also. If you get it painted, ask them how long the paint will stay on the bumper. Maybe the bumpers/side skirts can be replaced?
btw, I have a '97 honda and the bumper paint has not faded at all. The car is metallic light beige. I also had a '86 toyota van for 9 years (same color) and the bumper paint never faded.
2004 E60 530is, Delivered 12/12/03, TiSilver/LGrey, PP, SP,PS, PDC, ACC, FRS, Step, Xenons, clear bra, body colored rear inserts. (Retired, 1983 henna red 320is)
2004 Corvette Z06 Commemorative Edition