That orange looks surprisingly good!
I always use greens and blues on my bay with an occasionally turquoise. He looks awful in burgundy, purple or dull red. Bright red or black looks good on him for a saddle pad but awful in a halter.
Generally I pick a color I like and buy most things in that color for a particular horse. The rule is to stay away from colors that are too close to his color. The clash can be painful!
Even so, I'm like you, I seem to have ended up with a lot of different colors of tack anyway!!