So happy to see that my ribbon thread is remembered--thanks Prancingstag and Hathorcat!
I've had some ribbons cross my path that have that kind of fading/bleached look. Usually the pattern was on both sides, which makes it less likely the sun is the culprit, although the ribbons are probably thin enough that the sun could penetrate the ribbon and fade the opposite side. My guess is that the ribbon dye has become unstable and leeched out, possibly through getting wet or simply getting old. The ribbons I had that did that were blues, so maybe blues are just more prone to that.
Sundance's ribbon is a bit longer than usual and shinier, but I'm guessing it's not the one you have there.