Resistant to fading or running when exposed to light, water, or washing; able to maintain color over time and use.
Compound of 'color' and 'fast' (meaning fixed or permanent). The adjective emerged in textile manufacturing in the 19th century as synthetic dyes improved.
Colorfast is why modern red shirts don't destroy your white socks in the wash—it's a huge chemistry achievement that required developing dyes that actually bond with fibers instead of just sitting on top, and some vintage fabrics are actually more colorfast than modern ones because they used different (but better) dyes.
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