take a pic of the stitch card and post it so we can all see what we can choose from.
i know you want to enter this into a show so i would use a fancy type thread even though its not the best for day to day use.
i'm thinking red for directly on the boot (thats if you plan on quilting right on the boot) you could actually do the boot design by hand and mimic the fancy stitching on cowboy boots.
i'd use something to blend in on the background of the blocks and then for the brown sashing i used a variegated thread maybe red, white, blue.