Genetics: cm on C Locus.
Marten is recessive to the wild type (C) and incomplete dominant to the recessive C Locus alleles albino (c), Himalayan (ch), and Tonkinese (ct).
Marten the "red eyed devils" as they used to be known as is a fairly newer variety in which they have a darker colored rat with red eyes.
Marten was discovered in 2008 by René Bastiaans, he then named it RED or red eyed devil. Once the rats were imported to Europe in 2010 they were renamed to Martens, likely because of the stigma of the red eyed devil name, I would assume.
Marten only works on C Locus (so albino or himalayan). They can be Black eyed if they carry the Black Eyed (BE) gene. They can be many different colors but works best on dark colors.
As babies they can have a very unique and pretty marbled appearance, but this is actually not ideal. As they grow and molt their color fades some giving them this unique look. Ideally, we would want a non-pointed (so albino) dark dark black for a Marten to really have that striking black rat with red eyes appearance. But this can be a rare find these days.
Marten is not yet standardized by AFRMA
MARTEN - [Black] Body Colour to be similar in shade to an HB lead pencil, some fading to be expected in an adult. Some light heathering to be expected. Fur on the face to be lighter on the whisker bed, over the eyes and behind the ears. Belly colour a slightly paler shade of grey than the top. Foot colour to match top[Agouti; called Silver Agouti in N.F.R.S.] To be a mix
. Eyes pink. ofmid grey ticking over a pale ivory ground, with no suggestion of blue or brown tones. Ticking to be darkest along the back and to fade down the sides to the pale ivory belly. Fur on the face to be lighter on the whisker bed and around the eyes. Eyes pink.