Dilution

Some dogs are 'diluted' which basically means that their eumelanin pigment appears washed out. The dilution gene is called 'd' and appears to affect eumelanin more heavily than phaemelanin. Liver is sometimes called dilute, but that is not quite correct. Liver is caused by different genes.

A diluted black dog turns blue, ranging from a pale mouse-grey to silver to so dark blue it looks black at all times except perhaps in certain lights. The nose follows the shade of the coat but is never truly black (normally a dark smokey grey), likewise the eyes are amber or pale brown, but never truly dark brown like you may find in a black dog, though they can be surprisingly dark at times.
The dilution gene can affect liver, too. A diluted liver is usually called isabella (in some breeds the colour can be called for instance tawny or fawn) and is a pale creamy to grey-brown colour, most typically seen in the weimaraner. The nose is a fleshy colour, while the eyes are amber to yellow-grey.

 

A blue and tan tibetan mastiff

Isabella weimaraner

 

Tricolour (liver, creeping tan) rat terrier