Navy, always works for me! Black also and sometimes grey.
Navy and burgundy are great colours in my opinion. They seem to suit every horse colour.
Lime green on my bay and Dark Blue on my palomino
Definitely red it looks great on bays, greys, chestnuts
Black and white are obviously the most neutral colors. I personally don't think you could go wrong with hunter green or navy, though.
black and navy are my go to!
Maybe navy , dark red , white, and black might
I think Pale Blue suits a lot of colours.