Phaeomelanin
As you can see in this animation, if the MSH receptor on the melanocyte is defective, then MSH hormone cannot bind and phaeomelanin is produced and distributed into surrounding cells rather than eumelanin. This results in hairs with colors that range from yellow to red. Yellow Labrador Retrievers have a defective MSH receptor (due to the recessive 'ee' genotype at the extension locus) and thus produce only phaeomelanins in their coat.