If you are talking about the stallions halter classes, you probably won't see a lot of stallions older than 2 years old showing in the halter classes. I don't think the Fall Color Classic show is a big halter show to begin with...more people go there for the riding classes. I bet there were a few stallions shown under saddle. Several of the APHA shows I've been to this year have had stallions showing in the HUS or WP.
You won't normally see advertisements for stallions at the show. Stallion owners will promote their horses with full page ads placed in the Chronicle or PHJ, or maybe the NSBA magazine. They will have a website for the stallion & put promo videos on youtube. Many of them also participate in stallion service auctions & the associated futurity. Throughout the marketing material, the horses show record will be identified so people know what awards or big wins the stallion has won.