Cotton shop towels are often dyed red, like the one this dude is using to wipe down his impact driver (gotta keep those tools clean).
Why are shop towels often red? I'm thinking it's to make sure grizzly mechanics and maintenance folk are destined to have pink undies when they wash their unmentionables along with their shop towels.
Of course, your answer might be more plausible.
This article seems to think it's to cover up old dirt and grime which doesn't wash away. (NOTE: I don't agree with that for two reasons: 1) You can buy NEW rags fairly cheap. Most likely it costs as much or more to have old rags cleaned as it does to buy new. 2) The author of that article seems to be ragging on the rag industry ... I'm not buying what he says. Besides, I've never seen a cleaning company go back and dye the rags after cleaning.)
BTW, you can get these in other colors, like blue or white. Red is just the most prevalent. You can buy them fairly cheap brand new, then wash them yourself. Most are 100% cotton. Anyway, no real clue why, just chiming in.
To make them easy to spot if left under the bonnet so as not to cause a fire.
