I am a cool winter, and have always tended to favour black.
But I am working on expanding that.
So while most of my work trousers are black, I now have a navy pair and a grey pair. And I have a red suit but that is currently, um, rather too snug.
My winter "uniform" tends to be M&S ribbed woollen polo neck jumpers over plain trousers - but I have maybe 3 black, 2 navy, and then grey, bitter chocolate brown and red versions of the same jumper.
In warmer weather, I have a similar "uniform" of a Land's End long sleeved, round necked top (I have a few others from other companies, or with other necklines, but majority is this) - in black (about 4), navy (3), dark pine green (2), emerald green (2), burgundy, postbox red, grey, white (3).
I have a couple of bolero style cardigans that can go over those - black, navy, pine green, burgundy, white. And a couple of different jackets (black, pine green, white, white/black patterned, boucle navy/brown, tweed green/grey) and scarves/necklaces to ring the changes.
I also have a handful of dresses, mostly patterned but around those base colours (black, navy, reds, blue, some green).
Although I need to get a few more trousers and a suit (or lose a couple of stones).