Coloured patches appear on nylon and elastomeric parts of garments after being washed in a washing machine. This is due to the fabrics absorbing loose dyes from other garments in the same washing machine wash load.
Some garments when washed bleed a small amount of dye into the wash solution which usually has no or little effect on the colour of other garments.
However,nylon and elastomeric fabrics immediately absorb this loose dye and change colour.
Wash any garments containing white nylon in a "whites only" load.