I'm chief pegger outer and don't worry about the types or colour or pegs used. I'm a rebel, so mix them up and will fight anyone who criticises. :)
I know that woollies need 3 ..or even 4 pegs to hang them up so the don't dry with saggy parts. Jeans and trousers are 2 pegs (on the waistband). Socks (per pair) and underpants are 1 peg. Shirts and other non-stretchy materials can be just 2 pegs. A quadra-zillion pegs are needed for sheets so that they don't take off in the breeze or become detached and dangle on the ground.
Before this subject came up, I never realised there was so much science involved in hanging the washing out.