My favorite of the horse exhibitions we saw yesterday was this group of Roman Riders called the "Romanaires". They are a subgroup of the well-known Westernaires mounted drill team that is based out of Golden, Colorado and performs at rodeos all over the region. Although a few riders had horses that were well matched in color, most did not. I suspect it's much more important that the horses are roughly the same size.
The group did a lot of drill team work at a gallop. Their formations weren't always perfect, but I thought they did a really nice job overall. It looked like they were having fun out there.
I like this picture of these chestnut horses. Here's a close up of the tack. I think this would be very easy to make in model scale. There was some variation from pair to pair, but this was the general look--a cinched pad over a regular saddle pad, some sort of breastcollar with or without a running martingale, and a Western bridle or mechanical hackamore. All the riders wore tennis shoes.
I think this would be a really fun thing to set up in the model show ring. I have to admit that I'm eyeing my herd to see which two galloping horses would make a nice team...