I know most guys default to navy as the universal sock choice. I tend to default to charcoal grays myself. This is a charcoal wool sock from Byford. It has gold squares that picks up the colors in the shoes. I like that trick and incorporate it often in my sock selections. That is why I look for patterned socks that have spots of brown, tan, gold or rust...they all seem to compliment my brown shoes and the many pairs of khaki pants that I own. These shoes are from Sutor Mantellassi. I really like their casual style and the Norwegian welt.
I wear both jeans and grey flannels a lot. I will mix or match gray and navy socks with both. For about a year I have enjoyed the subtle elegance of solid gray socks with gray flannels. But every now and then, I will pair gray flannels with navy socks, especially when wearing a navy jacket or sweater.