The American Kennel Club (AKC) (and all other reputable kennel clubs around the world) recognizes three coat colors in the Labrador: black, yellow and chocolate.
A great article can be found HERE regarding health and behavioral issues in some of the dilutes.
A portion of the article states.....Various expressions of the dilution gene have been noted. Some dogs with dilute color display minimal or no health problems; other dogs experience hair loss and skin problems. Color dilution alopecia (CDA) and black hair follicular dysplasia (BHFD) can accompany coat color dilution. These diseases cause recurrent skin inflammation and drying, bacterial infections of hair follicles and severe hair loss. Other disorders that could travel with the dilution gene are heritable Weimeraner genetic issues such as trembling disorders, autoimmune related vaccination sensitivity and intolerance, Von Willebrands Disease, hyperuricosuria causing painful bladder and kidney disease, and behavioral problems that are more common in the Weimaraner, such as separation anxiety, and dominant, protective, territorial temperament. Minimizing occurrence of these conditions would mean minimization of the dilute mutation. Selection against dilution is important in breeds that display health issues associated with the mutation. It is also important to minimize the dilution mutation in breeds that do not have a standard written to include these colors. The Labrador Retriever is currently one of these breeds. Dilute colored Labrador retrievers are a disqualification according to breed standards. Those dogs carrying the dilute gene should not be registered as purebred Labrador Retrievers.