The dilute gene (MLPH gene) is responsible for the intensity of the coat colour by affecting the distribution of melanin-containing cells. This gene is also known as the D-Locus and dilutes all colours. Besides the hair colour also the colour of the nose is diluted and the colour of the eyes lightens to amber. The Coat Colour D-Locus Improved (MLPH) test (H847) tests for the genetic status of the D-Locus. The D-Locus has two variants (alleles). The allele D is dominant and does not have an effect on the coat colour. Only when the dog has two copies of the recessive allele d the coat colour is diluted. The dilution of black results in grey, also called blue or charcoal. The coat ranges from silver to almost black, but all have a blue nose. Chocolate/brown/liver dilutes into lilac/light tan/Isabella, their noses vary from pink, liver to isabella. Red/yellow/cream dilutes into champagne. In some breeds another, yet unidentified, mutation is present that causes coat colour dilution. This unidentified mutation is known to occur in Doberman Pinscher, French Bulldog, Italian Greyhound, Chow Chow and Shar-Pei.
The Coat Colour D-Locus Improved (MLPH) test encloses the following results, in this scheme the results of the Coat Colour D-Locus Improved (MLPH) test are shown in combination with the possible results for the E-Locus and B-Locus):
| D-Locus | E-Locus | B-Locus | Coat Colour | Nose/foot pads |
|---|---|---|---|---|
| D/D | Em/Em, Em/E or Em/e | B/B or B/b | Black, melanistic mask is not visible | Black |
| D/D | Em/Em, Em/E or Em/e | b/b | Brown/chocolate/liver, with melanistic mask | Pink to Brown |
| D/D | E/E or E/e | B/B,B/b | Black, no melanistic mask | Black |
| D/D | E/E or E/e | b/b | Brown/chocolate/liver, no melanistic mask | Pink to Brown |
| D/D | e/e | B/B,B/b | Red/Yellow/Cream | Black |
| D/D | e/e | b/b | Red/Yellow/Cream | Pink to Brown |
| D/d | Em/Em, Em/E or Em/e | B/B or B/b | Black, melanistic mask is not visible | Black |
| D/d | Em/Em, Em/E or Em/e | b/b | Brown/chocolate/liver, with melanistic mask | Pink to Brown |
| D/d | E/E or E/e | B/B,B/b | Black, no melanistic mask | Black |
| D/d | E/E or E/e | b/b | Brown/chocolate/liver, no melanistic mask | Pink to Brown |
| D/d | e/e | B/B,B/b | Red/Yellow/Cream | Black |
| D/d | e/e | b/b | Red/Yellow/Cream | Pink to Brown |
| d/d | Em/Em, Em/E or Em/e | B/B or B/b | Blue/Grey/Charcoal, melanistic mask is not visible | Blue to Black |
| d/d | Em/Em, Em/E or Em/e | b/b | Lilac/Light tan/Isabela, with melanistic mask | Pink to Brown |
| d/d | E/E or E/e | B/B,B/b | Blue/Grey/Charcoal, no melanistic mask | Blue to Black |
| d/d | E/E or E/e | b/b | Lilac/Light tan/Isabela, no melanistic mask | Pink to Brown |
| d/d | e/e | B/B,B/b | Champagne | Blue to Black |
| d/d | e/e | b/b | Champagne | Pink to Brown |