The blue colored varieties have existed in the Marans breed since its origins, i.e. Blue was introduced at the first crossing with it’s English Game ancestors. At this time I can find no country that has accepted a Blue or Splash as a separate variety, but the process is under way in several. The Blue gene is a dominant gene with variable penetration that dilutes black pigment, when present in either the homozygous Bl/Bl, or the heterozygous Bl/bl+ states. In the heterozygous state, Bl/bl+ dilutes black to a bluish/gray color, this blue color produces a variety of shades in the plumage, ranging from ‘pigeon egg blue’ to a dark ‘navy blue’, often with some blackish feathers scattered here and there, but has no effect on gold/red pigments. Homozygous Blue Bl/Bl creates an even greater dilution effect, producing a Splashed White (Splash) bird. This plumage is white with the odd blue feather; it is known in Europe as “dirty White” This is very different from both the Dominant White and the Recessive White, both of which have the effect of converting black to white.

It is important to understand that:

Blue does not breed true but gives the following results,

A Blue to Blue, Bl/bl+ X Bl/bl+ mating will give 25% Splash, Bl/Bl; 50% Blue, Bl/bl+ and 25% Black bl+/bl+

A Splash to Black, Bl/Bl X bl+/bl+ mating gives 100% Blue, Bl/bl+

A Blue to Black mating, bl+/bl+ X Bl/bl+, gives 50% each Blue, Bl/bl+ and Black bl+/bl+.

Blue should not be confused with recessive Lavender, which dilutes both black and red, and is true breeding. Lavender dilutes black to a "pearl gray color" producing a very uniform plumage colour. The  "pearl-gray color" is not found in Marans.

The genome of the heterozygous Blue Marans cock is E/E S/S Ml/Ml Bl/bl+ Id/Id W/W Pti-1/Pti-1 and that of the hen is E/E S/- Ml/Ml Bl/bl+ Id/- W/W Pti-1/Pti-1.

The varieties based on the Extended Black allele may mask all other allele in the series.