If you are planning on showing at all, be cautious as many of the color enhancing supplements contain things which will test positive in a drug test.
Any spice containing capsaicin will also test positive.
Well, shazam! Learn something new every day. Paprika for coat color. Hmmm, I wonder what it would do for me? I'd probably end up looking like I had liver failure instead of changing this grey hair to auburn.
Anebel's advice is good. Make sure whatever you feed it won't get you tossed from the show ring.