Blue eyes are rare, if not nonexistent, in purebred chocolate Labrador Retrievers. The breed standard calls for a chocolate Lab to have brown or hazel eyes. Labs are not known to carry the merle gene that is often responsible for blue eyes in dogs.
Besides the merle gene, blue eyes can be associated with large amounts of white around the eyes and with mutations of a gene regulating the structure and function of tyrosinase. These genes affect both coat and eye color. Labs lack extensive white spotting in the fur and the blue eyes associated with it, but it is possible that some breed lines carry a mutant form of the gene regulating tyrosinase. This gene lightens a chocolate coat and could result in blue eyes.