I made my first real quilt in 1970 and many since. I've never had a quilt fade. It isn't the fabric, but the after treatment. quilts on the window side of a bid will fade, hung quilts can fade. I had a cotton blouse fade in the shoulders and front in a week in Texas sun.
If there was/is something to make fabric colors more permananat the mfgrs are already doing it with chemicals/dyes/fixatives. Not things consumers can lay their hands on.