Some steps improve rabbit coat color, and softness.
DO NOT wash your bunny unless it has gotten into something and gotten its coat filthy. It does nothing to improve a coat for show and if a judge feels that any sort of grooming product you use has left any residue on the coat, he or she can disqualify your entire entry (not just the animal in question). Do groom the coat with a natural bristle brush or with your damp hands. Be sure the coat is dry when she hits the table. We judges do not take kindly to anything done to an animal that alters its natural appearance.
A good quality pellet is the most important thing to make sure that your rabbit is in top condition. Some exhibitors use a bit of sweet feed or rolled oats in addition to pellets and hay. We have not found much improvement in condition with it and there is a tendency for them to put on some weight with these supplements.
Frankly, if your rabbit is fit, you have done what you can do. Coat quality, body type, bone structure, color, ear length, head type, etc are things you fix in the breed pen, not the feed bucket.
Do not feed seeds or nuts. They are very fattening and Dwarfs have a top weight limit. If they are fat, rather than fit, it is really easy for them to go over weight. No serious rabbit exhibitor feeds any fresh veg. It is almost impossible to keep firm flesh and a flat belly when feeding veg. The one exception is a bit of carrot, sweet potato or similar stuff in the carrier while traveling for the moisture since most bottles leak when the vehicle is in motion and can't be used.