Okay, you're doing great! I have to take everyone's word for it since I don't know western movies at all but I'll run some of these by him. Keep 'em coming though! I think so far my favorite is Blaze. I was thinking about the red merle aspect and thought of "Scarlett" from Gone With the Wind but I'm not really sure you'd consider that a "western" really. I eagerly await more ideas...
By the way, the reason he's going "western" is for the most part because him and his uncle do chuckwagon cooking competition plus he really likes western movies. Just in case you wanted some background!