I don't see a problem with it. I have seen a lot of horses in brown dressage saddles
My old dressage saddle was brown and I was showing 3erd level with it and prelim horse trials. No one said anything.
The most important thing is that it is clean and your bridle matches and you are well turned out
I do want to say your flash is sitting to low in that picture. The caveson should be done up a bit higher under the cheek bone. Where the flash is sitting can restrict breathing.
On another note... I LOVE your horse. His(?) face is beautiful.