Red could possibly be short for Redford or Redmond, but it's almost always a nickname for a person with red hair. As such, it's a very dated, downmarket kind of nn, along the lines of Shorty, Slim or Blondie.
"It's one thing to be open-minded and quite another to be so open-minded your brains fall out."--Dear Abby
"Let other people push you around, and you deserve whatever bad things happen after that."--Lauren Bacall