Thanks for the suggestions, guys.
FYI, I was able to go to wetokole.com and search for "21-21-11P" and "11-11-21P" to see examples of Light Gray (#21) with Charcoal (#11) piping and vice versa. So the code seems to be <Outside>-<Inside>-<Piping>P.
I couldn't find any examples of 21-21-23P or 11-11-23P but when I searched for "23P", I did see a 12-12-23P (#12 is black). It may just be the contrast with black but the blue seems really apparent. I was hoping for something more subtle. Tough to be that adventurous without having the car in front of you.
Still debating...