I'm not one who has to have everything matching, or really a color theme for each horse. However, I am a big fan of fun and bright colors in general.
My Palomino wore blue most of the time. I love yellow though, and it's the worst possible color with palomino, so now that I bought a new horse that's seal brown (nearly black) I'm using some of that. I made him blue and yellow reins, and just bought yellow polos :). He's also super cute in blues, and I guess burgundy is my preferred "conservative" color.
You know the Amigo blankets that come in all the unusual colors? Love them! My horse has one red and one baby blue (and I would love the green). I love seeing him out in the field like that...his navy blanky bores me and makes me sad.