Or just do what I do, after washing/drying, throw them all in a heap on the floor and tell them to find their own socks & pair them up.
DD never wears a matching pair, she'll have grey with spots on one foot and pink stripes on the other, but she's happy.
DS2 has days of the week so he knows which are his and it means I know he's changed them every day!
DS1 is so horrified at the thought of accidentally ending up with some of DP's that he will meticulously check which black socks are his and which are not.
DP has all plain black ones, but as Quint says, they are all slightly different shades of faded black, slightly more or less stretched etc. A nightmare to try and pair into actual pairs. I don't think he minds and he says it helps if one gets a hole in, he only has to throw away one not both, but it winds me up!