An extract from Debrett’s Guide for the Modern Gentlemen:
“There is one essential rule for socks: they should always be long enough. That means that, when you cross your legs as you sit down, an inch or two of calf flesh should not suddenly appear underneath your trousers.
In terms of colour and pattern, however, there are two schools of thought. One is that, no matter what, your socks should be plain, unpatterned and preferably black (unless, you are wearing a brown belt, in which case they should be brown or possibly grey).
The other opinion is that they are a chance to add some sparkle. Some people like to have a bit of fun, and add some flash. It is, however, really up to you, but go for spots or stripes and never wear novelty pairs featuring cartoon characters.
Socks can also be matched with your jacket and tie; some say you should also match them to your belt, but that’s not to everyone’s taste.
While, once, the rule used to be ‘wool for winter and cotton for summer’, good quality, thin, cotton socks should be adequate for most of the year.”