Photo curtesy of Armour Rattery

“… a deep, dark gray in black based rats that is described as between Russian Blue and Black. On an Agouti background it is assumed to have the appearance of sand…”

The Sd Locus

Midnight Blue is a bit of a mystery at this time, with very few breeders having worked with it in recent time and even less working with it currently. The few times it was documented by breeders, it was speculated that Midnight Blue may very well be the black dilute of the Sand mutation. I don’t believe this was ever confirmed or even if it truly could be, however the gene symbol being used for Midnight Blue is due to this. There is also a color known as German Blue, but no information available in the US other then some descriptions that sound fairly identical to the Midnight Blue. At this time it is unknown if they are allelic as test breeding has not been done but it is sometimes assumed they are the same mutation.

The Sand gene creates a deep, dark gray in black based rats that is described as between Russian Blue and Black. It is a flat, even coloring with lesser of a blue tint. On an Agouti background it is assumed to have the appearance of sand based on an article on melanistic rats. Shadow and melanistic rats are assumed to be one in the same, and seem to be tied to the Midnight Blue and Sand color dilutions. Though it is recorded the mutation can be separated from each other it is pretty rare at the time and almost no information is recorded on it without being in a Shadow line.


In January of the year 2000 Alan diGani of Fith Fath rattery breed an unusual black rat named Martine, and she would be the start of his Shadow line. After several generations of inbreeding the Midnight Blue mutation appeared.

At first assumed to be a very dark Russian Blue, it was soon determined through to be on a different allele when several black babies were born of Midnight and Russian crossings. It was noted in diGani’s article that a color dilution was as well seen to pop up in the melanistic rats found outside the Oklahoma City Zoo, and was described by Randolph M. Macy and Allan J. Stanley in an article as Sand due to it’s appearance on an agouti rat. They performed many test breedings and sets the earliest discovery of this mutation to 1973.

Unfortunately there is no recorded information of further testing I could find about if the Sand coloring comes up when crossing Midnight Blue with Agouti, but as it seems likely we will use the symbol until it can be tested.


Currently there’s very little information about cross-genetics that involve Midnight Blue. There is probably a connection between the Shadow/Melanistic mutation and Midnight Blue/Sand, as this color dilute seems to pop up wherever Shadow is present.

In diGani’s article he talks about several cross-genetics but there are not colored pictures to go along with them. Mixing with the other blue genes basically fills in the gaps of shades between them from what it seems. Caramel seems to also be an interesting color derived from Mink dilution. Lastly a Dark-Eyed Silver is mentioned, that does sound quite stunning and could appeal to pet owners.


            AFRMA [US] 







  • The Sd locus is recessive.
  • Midnight Blue seems to be related to Melanistic/Shadow rats.
  • The Sand allele was first discovered in 1973.
  • This gene though rare and mostly unknown has popped up several times in rat history.


A Final Thought

This color really intrigues me, and I can’t wait to be able to work with it. I will be working on getting the Midnight Blue and Shadow lines some time later in 2021, though I do have a few leads at where I might be able to get them and hopefully once I built relationships with new breeders this options opens up in short time. I have since acquired a male Midnight Blue breeder and I can’t wait to start test breeding with him to find out more about this color and any unique combinations we may be able to discover.