Shoppers looking for their next great outfit make their selections on the basis of colour, cut, style, and price. They may not know that dyeing clothes requires massive amounts of water, energy, and chemicals. Those chemicals are released in wastewater from dye houses and textile mills. Reports of rivers with unnatural hues have inspired government crackdowns and sustainability pledges from international apparel brands. But changing this $3 tr industry will require innovation that can be scaled up and adopted without cost or disruption for manufacturers.