The AKC Labrador Standard

"The Labrador Retriever coat colors are black, yellow and chocolate. Any other color or combination of colors is a disqualification. A small white spot on the chest is permissible, but not desirable. White hairs from aging or scarring are not to be misinterpreted as brindling. Black— Blacks are all black. A black with brindle markings or a black with tan markings is a disqualification. Yellow—Yellows may range in color from fox-red to light cream with variations in shading on the ears, back, and underparts of the dog. Chocolate—Chocolates can vary in shade from light to dark chocolate. Chocolate with brindle or tan markings is a disqualification." 

"Size-The height at the withers for a dog is 22½ to 24½ inches; for a bitch is 21½ to 23½ inches. Any variance greater than ½ inch above or below these heights is a disqualification. Approximate weight of dogs and bitches in working condition: dogs 65 to 80 pounds; bitches 55 to 70 pounds."

"Temperament: True Labrador Retriever temperament is as much a hallmark of the breed as the "otter" tail. The ideal disposition is one of a kindly, outgoing, tractable nature; eager to please and non-aggressive towards man or animal. The Labrador has much that appeals to people; his Page 4 of 4 gentle ways, intelligence and adaptability make him an ideal dog. Aggressiveness towards humans or other animals, or any evidence of shyness in an adult should be severely penalized."

"Disqualifications: 1. Any deviation from the height prescribed in the Standard. 2. A thoroughly pink nose or one lacking in any pigment. 3. Eye rims without pigment. 4. Docking or otherwise altering the length or natural carriage of the tail. 5. Any other color or a combination of colors other than black, yellow or chocolate as described in the Standard."

From the AKC website. Visit their website for additional information.