The American Kennel Club, sez; "The nose should be wide and the nostrils well-developed. The nose should be black on black or yellow dogs, and brown on chocolates. Nose color fading to a lighter shade is not a fault. A thoroughly pink nose or one lacking in any pigment is a disqualification." http://www.akc.org/breeds/labrador_retriever/index.cfm I guess an AKC show would be "mainstream." Sometimes various organizations, clubs, breeders societies, SPCA's etc, that may or not be associated with the AKC sometimes hold what could be called "Fun Shows," that might not follow all the standards. That might be a non-main stream show. There are also 'field trials', especially for sporting dogs such as labs. Some trials are AKC sponsored or otherwise assocciated with the AKC, some of the trials are open only to dogs that meet the breed standards, some dogs become double champions, winning both trials and shows. Other trials are open to dogs that don't meet all the standards, nobody cares what color the dog's nose is. All they care about is how good a job the dog does retreiving "ducks" from the water. Those 'shows' could be held on the mainstream or a tributary or even a swimming pool.