First and foremost, I should point out that the below are not ‘rules’, nor even ‘guidelines’, but more thoughts that might help you make different decisions. Choosing socks to go with an outfit is not something that needs to be regulated; it is something to have a bit of fun with. So, be flexible but bear the following in mind.
Black socks are formal. They should are ideal for ‘occasions’, be they black tie events or just dining somewhere swanky with someone special. Much like black suits in that respect – worn past 6pm they can look dapperlicious, but before then (excepting funerals), they seem somehow inappropriate. In keeping with the formality of black socks, a silk mix is just the ticket to add some Style Points.
If you’re going matchy-matchy with your socks, go matchy-matchy with your trousers, not shoes. This is a handy tip if you don’t want to incorporate more colours into your look. Otherwise, it’s playing it a bit safe: not very dashing or debonair, more dependable if you catch my drift.
Assuming you’re interested in pushing the bounds of the commonplace just a little, socks are a great way of instilling an outfit with a little more colour without being ostentatious or over the top. Discreet elegance is the aim, not attention-grabbing and not – Heaven help us – ‘in your face’.
A navy suit might be a typical City outfit. Pretty much any shade of red or purple would look fantastic with this. If a tie or pocket square is not worn (as seems to be the trend nowadays) or if no new colours are introduced (if, say, the tie is a shade of blue or the pocket square is white like the shirt), there are not many limits to the colours you can incorporate.
If wearing a different colour tie or pocket square, try to pick socks that work well with these other accessories. Sticking with our aforementioned navy suit and black shoes, for example, you might choose a pink tie (or a tie with pink in it). Purple socks might pick this out but red socks might clash.
Grey suits can be treated as above but with the addition of navy and green socks (save the green for less formal suits, perhaps). Grey is a very flexible colour in almost all of its shades (charcoal suits can be tricky, wear darker shades of socks). My personal favorite is a deep red with grey, and brown shoes. The red provides a jolly good frame to highlight the brightly polished shoes and the footwear takes on a chestnutty hue.
If wearing a grey suit with coloured accessories, and so not wanting to add another colour, mid-grey socks are ideal. Many English style icons of the 50’s and 60’s (in those blessed days before cartoon characters appeared on hosiery) often would wear pale grey or a pastel colour with tweed, flannel or heavier wools.