"as long as the bridle and saddle are the same color"
Nope. Absolutely nope.
"black is the more modern color"
Brown, actually, is quite fashionable and has been for a good many years - as long as I've been into dressage - over 40 years in fact. People tend to like colors that go with their horse. And for example brown can look lovely on a horse with brown tones in its coat.
No rule says ANYTHING about tack color specifically, and judges, in book after book, article after article, seminar after seminar, clinic afer clinic, have stressed again and again to the point of practically pulling out their hair and screaming, that dressage is not a tack or beauty contest - they do not care if your bridle and saddle are same color, if brown, if black - NOTHING.
Buy the saddle color you like. That's all there is to it. Have a brown saddle, black bridle, brown jacket, WHATEV...these guys simply DO NOT CARE - in fact, they have gone to great lengths to say that you will place based on your riding and training.
In fact the judges are very, very adamant that they NEVER want dressage to be a beauty or tack contest
, not in the least little tiny way.
People often say, 'well well, you know, it makes an impression, and even the judges themselves don't realize it affects their judging'. Baloney. Exactly the opposite. The judges go out of their way to not have it affect their judging
The rules for dressage tack and bitting and even rider clothing are very, very vague and general.
I would not go out there and try to break the rules that are there in some completely outrageous way, but the rules are few and very, very simple.
And I'd also suggest you follow the general trends out there that aren't included in the actual rules, just so you do not feel out of place when you go to compete.
I would suggest you very, very much go out of your way NOT to arrive in the ring with a filthy horse and dirty tack, and that you clean your boots off and don't appear in the ring as if you have no respect for the judge, the sport, yourself or your horse.
But even the general trends, that are not in the rules, are very, vey simple - and people compete in brown saddles, and in brown bridles with black saddles, and black bridles with brown saddles - ALL THE TIME.
Your personal taste may be that you like or don't like certain colors or combinations, but that has nothing to do with how you will be judged.
The take home point is that dressage judging simply is not about fashion issues!!!