Why does the zipper colour fade after washing?

Q: Why does the zipper colour fade after washing? Colour fade on a zipper tape can come from dye fastness, from the wash condition, or from both. A controlled comparison between washed and unwashed tape, and between tape and shell, separates the possibilities quickly. Wash a loose length of the same tape with the garment and compare with an unwashed control. Check the wash temperature, detergent type and use of bleach or optical brighteners. Compare the tape with the shell fabric to see whether the fade is uniform. Ask the maker for the fastness data for the specific colour and tape. Repeat a wash at the care-label condition to see whether fade still occurs. Fade in the loose tape as well as the sewn garment points to the tape or the dye and should go to the maker with the colour reference. Fade only in the garment points to the wash route. Judge against the approved standard under a fixed light, because colour memory is unreliable and two observers will otherwise disagree.