Cool! Dressage and Working Equitation!
My opinion for your handsome boy:
With the green pad, I think I would go with tan breeches to match your guys warm tan tones. I would consider a nice burgundy coat, which is also a “warmer” color and I think would look fab with that green pad. Alternatively, I’d stay with the tan breeches instead of grey and consider a nice darker blue jacket. Not navy, but more of a Royal-ish blue or lighter shade of Royal-ish blue. That would also look great with that green pad. AND the orange pad. And would go nicely with your horse’s tan coat.