I prefer the blue
I personally think that most chestnuts don't look good in black (don't know why, just doesn't appeal to me) but I do like the look of the black pad on your horse with your brown tack. I love black anything on a bay, buckskin, or similar, but black and red wouldn't be my first color choice if I had a chestnut.I really like the (blue) pad in the last pic. I only used the black (which is really just a pad to go under other thin blankets) because I didn't have anything to match the blue shirt, but I kind of like it with the blue too. This may sound weird because I bet most horses look good in black, but I've always thought that black looked really sharp on him. That was random.
Honestly, I don't know anything about western shows. Best to ask someone else about proper show attire, but I don't think there's any show in which jeans would look better than black pants for a finished lookThanks guys for the suggestions! TheChelseyDee and DuckDogger, you both mentioned the black pants- are you talking about show pants? Would that be appropriate at small county shows?