A colorado tux is a blue blazer over a button down long sleeved oxford shirt on top, and jeans and cowboy boots beneath that.
The blue blazer can come from any department store; the oxford has to be 100% cotton, and pressed; ideally the jeans would be Wrangler, because that's what real Colorado cowboys wear; and the cowboy boots have to be pointy, and can't be one of those new fangled pairs with laces.
It can be accessorized with a wide brown leather belt, hopefully with leather stitching along the edges, and with a big shiny rodeo belt buckle. A cowboy hat of any kind is also a good accessory.
At the opera in Denver: "Look at all the Colorado tuxedos. That's about as nice as people dress around here."