But back to why your shirts seem to yellow so very quickly in the first place. While bluing went out of style as a household product in the '70s, it only got more popular with textile manufacturers. They want to make sure their Egyptian cotton towels are the whitest on the shelves, so companies blue their whites before they send them to stores to give them that extra oomph of whiteness. Alas, bluing doesn't last forever. It actually only lasts a few washes, at which point the cotton reverts to its original hue. Processed, bleached cotton's natural color is not that yellow, but compared to how white those towels were when you bought them, they look pretty dingy now, don't they?