My fabrics are all stored in frosted clear boxes out of direct sunlight, but in an open studio with windows on two sides. In more than 15 years like that, I have noticed no color fading whatsoever even of the deepest colors.
Once the fabrics are put into quilts, they will not be kept hidden away in dark closets, so I'm just not going to worry about it. Storing them on wooden shevles does far more damage than in clear boxes.