Should your socks match your trousers?
In formal wear, yes. Matching socks will also elongate the leg – just make sure you’ve got the right tone. Blue-black trousers with a warm black sock won’t look right. The rules relax for jeans or chinos: go for the complementary or contrasting colour route; you can also have a little fun with pattern.
What colour suits work with what colour socks?
There are a few sure, solid choices. Unexciting, but a black suit can only safely stand with a grey, black or navy sock. Perhaps push the envelope with a muted wine red. All of the above will work with a navy suit, as will brighter blues or darker browns, greens and dusted shades. A grey suit allows far more variety in colour choices.
What about matching with your shoes?
Bizarrely, given their proximity, your shoes and socks bear little relation to each other colour-wise. Your socks should never match your shoes unless you’re wearing very pale trousers, and even then you should go tonal, not matching. If your shoes match your socks, you aren’t doing justice to either.