They fade no problems....
Ari always does fluro orange poos and the stains are almost always gone after one hang outside, if not then by the next wash they are fine.
I hung Ari's BG microfibre insert, which was very orange, outside (well, undercover on our deck as its cold and raining) 2 days ago....brought it in today with not a mark
There are still UV rays when it is cloudy.