Having put myself through
university by working in the construction industry, I can honestly say that I've never heard the words
red cunt hair ever used to describe anything other than a red cunt hair.
However, I have often heard the more abbreviated version, cunt hair, used as a synonym for "a little bit". I myself used the term quite often; partly because it was kind of fun to say and partly out of survival. It might sound a little harsh, but you've got to understand that walking around a construction site wearing your school t-shirt and using cutsy, high-falootin' words will only result in you getting a hammer up your ass for your troubles.
Observe:
"It that stud level?"
"Move it a teensy bit to the left and you've got it."
"Whut?"
"I said: A weensy bit more and you've got it."
"Let's try this again, college boy. I asked you if that stud was level."
"Sorry. A cunt hair to the left and that sonofabitch will be right as rain. Hey, did ya catch the game yesterday? Can ya believe those fuckers lost again? Damn, I could use some poontang. You guys wanna a grab a beer after work? Fucking Christ it's hot out here."
"Shut up"
"Okey-dokey."
"Whut?"
"Fuckin-A!"
/me gives the thumbs up and wonders if anyone has ever succesfully killed their foreman with a nailgun.