Nylon. It is an interesting fiber. It is man made, synthetic, and has a unique property whereby it attracts and absorbs dye readily. Which is great, because that means it is one of the only synthetic fibers that can be dyed at home. BUT, it also means that if you wash a nylon garment, let's say two pairs of pink tights, in a washer which also contains dark colored garments, let's say two black leotards, then your nylon will suck up as much of the dye the dark colored items shed as possible.
Which I know, because I was the first person in something like five years to graduate from Textiles class with an A. And also because I was a total idiot yesterday and washed all my delicates in the same load. And now I have peachy-gray tights to wear to class.