Why Are My Nylon Workouts Clothes Turning Pink After Washing?

All of our nylon white workout clothes Underarmor, Nike, etc. are turning pink. They are not being washed with other red things and the rest of the clothes and towels and cotton whites are fine, it is only the nylon stuff. I switched to Gain laundry detergent, do you think that is it?

By Janey from Murrieta, CA