You definitely do not have to have show colors. Generally if you are going to a horse show that is USEF related or something at or above regional level, you don't want colors on your horse. Having dark brown/black tack and no crazy colors is the best. If competing at one of these competitions, the best option is to wear a solid black or white saddlepad, if you must wear polos, wear black polos for bay horses, and also if at all possible, wear a white shirt and black/dark green/blue hunt coat. This will give a great impression to the judges and other horseshow exhibitors. Crazy/ matching colors can be fun at 4-h or non rated shows, but for larger sized horseshows it is best to have formal attire.
I don't have show colors. In the hunters and Eq nothing is colorful.
No, up to you. Sometimes it's just a bit more fun to have colours but it's optional
No you have to. I keep my colors black and white.
I think it depends on the show. I don't really tend to have show colours and just make sure the stuff I'm showing in is clean