https://www.guidingeyes.org/21268/black-and-tan-labrador-retrievers/
http://www.chessieinfo.net/chesapeake-bay-retriever-coloration.htm
http://www.thelab260.com/YellowLabradorRetrievers/yellow-eyes-labrador-retrievers
http://www.retriiverid.ee/aretus/karvavarvuste-parandumine/
https://www.flickr.com/photos/14122456@N05/6887540766
Color Morph Series: Tan-point Labrador Retriever
Black and tan coloring in Labrador Retrievers is due to a recessive gene
that each parent must contribute. When both parents have contributed
the gene, the pup has lighter tan colored fur above the eyes, around the
muzzle, on the chest and legs.Black and tan […] Labradors can be registered with the American
Kennel Club, but they can not compete in the show ring as these colors
are considered undesirable to the breed standard.– source