Like others my first thought was possible color blindness. We had one female customer who was color blind, very unusual for a woman. But she saw value - grays, blacks & white. She had to trust other to pick her colors for her.
Has she asked for help? Has she commented on the appearance of some quilts? Perhaps wholecloth quilts or monochromatic quilts.
Value: You can make a black & white copy of fabrics and study how light/dark they are. I sometimes scan them and change the jpg to grayscale.