A Primer on the Genetics of Color
Breed Standard: The Labrador Retriever coat colors are black, yellow and chocolate. Any other color or a combination of colors is a disqualification. White hairs from aging or scarring are not to be misinterpreted as brindling.
Black - Blacks are all black. A small white area on the chest is permissible and sometimes, will fall out with the puppy coat. This comes from the ancestor of the Labrador Retriever, the St. Johns Water Dog. The earliest photo of a Labrador Retriever is of "Nell" taken in 1899 (see "Know Your Breed"). You will also sometimes see white spots on the feet; this is found in the descendants of English Dual Champion Banchory Bolo (1915 – 1927) and are called "bolo marks".
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. There is no such thing as a "White" Labrador; it is a Yellow Lab with a white or cream colored coat; likewise, there is no such things as a "Fox Red" Labrador; it is a Yellow Lab with a red-ish coat. A Yellow Lab with a dark chocolate nose is actually genetically a Chocolate dog with a yellow coat.
Chocolate - Chocolates can vary in shade from light to dark chocolate; a white "ring" around the tail is common and typically falls out with the puppy coat. Chocolate with brindle or tan markings is a disqualification. Chocolates have "chocolate" noses (formerly called Liver), eye rims and pads.
Disqualifications from the Breed Standard
A black with brindle markings or a black with tan markings is a disqualification. (A small white spot on the chest is permissible.)
A thoroughly pink nose or one lacking in any pigment. (Traditionally called a "Dudley".)
Eye rims without pigment.
Any other color or a combination of colors other than black, yellow or chocolate as described in the Standard.
Phenotype is visible while Genotype is invisible and determined by what is inherited from the Dam and Sire.
A dog has two versions of each color gene receiving one from it's Dam and one from it's Sire. A capital letter indicates a dominant...i.e. "B" (Black) is dominant and cancels out "b" (Chocolate) while "E" is dominant and cancels out "e" (Yellow). The gene loci for Color control both the color of the pigment as well as the distribution of melanocytes throughout the body of the Lab.
At the "A" Locus, there should be a Dominant/Recessive carriage of As. If this combination is not found, there is a chance that a white spot on the chest, or feet, or under the arms and legs will be expressed. Therefore, white mark on a Black Labrador’s chest is not as unusual as you might think, in fact it resembles the St John’s Water Dog, an ancestor of the modern Labrador breed. Due to the size of the Black Labradors’ gene pool (solid Black was the goal of all the earliest breeders and remained the most popular color for generations), the white spot is just no longer as common as it was when the breed was much younger.
Black Dogs can be: BBEE (no hidden colors) or BbEe (hidden chocolate and hidden yellow) - With no test available as of now for the As confirmation, the white spot will not be expressed unless two dogs who both carry something other than As are bred together.
Chocolate Dogs can be: bbEE (no hidden colors) or bbEe (hidden yellow) OR bbee (chocolate pigmented yellow coat) - As with the Black Labrador, there is no test for confirmation of the As combination available at this time (see above).
Yellow Dogs can be: BBee (no hidden chocolate) or Bbee (hidden chocolate) OR bbee (chocolate pigmented yellow coat) - In Yellow dogs, the white spot is expressed more often but not visible without close examination as the shading of yellow can go from white/cream to fox red. It will be more visible in the fox red coat.
A dog that receives a "b" from both it's Dam and Sire is Chocolate with no Black anywhere (bb)- including nose, lips and eye rims. Our Little Cain is a bbEE (or EEbb) mating him with a Yellow or Black female will never produce any Yellow puppies while mating him with a Black will produce Black and Chocolate puppies depending upon the Black's genotype. A dog that receives a "b" and an "e" from both parents has no black pigment; it needs at least one "B" to have the Black nose, lips and eye rims which is the desired state according to the Breed Standard, a chocolate nose on a yellow is "fault" not a disqualification however a nose "thoroughly lacking pigment or flesh colored" (pink) are a disqualification, as are a eye-rims with no pigmentation.
A dog that receives an "e" from both parents is Yellow coated (ee); it's nose and eye rims are determined by whether it received a "B" from either parent. All of our Yellow Labradors are BBee (eeBB). Mating them with a Chocolate will never produce a Chocolate puppy. Mating them with a Black will produce both Black and Yellow puppies depending upon the genotype of the Black (a BBEe Black will produce both Black and Yellow puppies with one of our Yellows/a BBEE Black will produce only Black puppies with one of our Yellows). Mating two of our Yellows to each other (a BBee to a BBee) will ONLY produce Yellow Labradors with Black pigment. We do not produce Dudley's here at Aisling.
With the ability to genetically test coat colors, Breeders now can breed Yellow to Chocolate with no worries about producing puppies who would be disqualified from Conformation Competitions for a nose or eye rims lacking pigment. (Go here to read more about the loci responsible for the far less common Brindle and Tan Point miss-markings in Labradors.)
For a visual reference, see "Coat Color Inheritance Chart For Labrador Retrievers".