pink nose/ liver nose

Question
how do yellow labrador's noses turn pink or a liver color?

Answer
I don't know exactly how, but it has to do with the sunlight they get.  Some yellow Labs' noses fade is they don't get enough sunlight.  The body must need the stimulus of sunlight to to produce the black pigment.  Some yellow Labs noses always stay black or pink whether they are getting sun or not.