Dilute Locus (Blue) Also called the "blue" locus. The recessive allele at this locus changes black (eumelanin) pigment to dark slate gray wherever it appears on the dog. It also takes the red out of the red/yellow (phaeomelanin) pigment, lightening it somewhat and making it appear dull.
The dogs in the front are blue. Compared to the dark gray (left) and Seal (right) in the rear, you can see the blue's coat color appears paler and slightly washed out.
You can see the slightly washed out pigment on the noses and eye rims of these two Blues, as well as the gray or hazel eyes.
Pigment on the pads is also affected by the dilute locus.
d - Dilute (we call them Blue)
The black band is changed to dark slate gray. Pigment on nose, eye rims, lips, and pads is also changed to dark slate gray. Eye color is yellowish or hazel, sometimes with a gray or bluish cast.
D - Black or Non-Dilute
The black band in the coat as well as nose and skin pigment is unaffected and remains black.