The particulars for the markings of Berkshire rats vary from country to country. In the UK, the preference tends to be for a rat with a large white marking over the belly and chest, which may or may not be connected to the white on the leg markings by a small white line. The American Berkshire aims for a rat that is entirely white on the underside, including the inside of the legs and the underside of the head and neck. The term Berkshire itself is borrowed from the breed of pig.

Berkshires with blazes are referred to as Badgers. Poorly graduated Essex rats can be mistaken for Berkshires – and can do quite well at times, since they tend to have the headspot that’s so prized on Berkshires.

Genetics: Generally Hh, HHre, Hhe or similar (one copy of the H gene plus another h allele).

NFRS standard: To be symmetrically marked, with as much white on the chest and belly as possible. The white shall not extend up the sides of the body; the edges shall be clear cut and devoid of brindling. Back feet to be white to the ankle, forelegs to be white to half the leg. Tail to be white to half its length. The body colour shall conform to the recognised colour variety. The white area shall be pure and devoid of any colour or staining. A white spot on the forehead is desirable. Suspenders to be allowed providing they are symmetrical.

AFRMA standard: Berkshire rats may be shown in any recognized color. The top color is to be judged as to the recognized color. Distinctive markings are the colored top with a completely white belly and white feet and tail, with a small white spot between the ears. There should be an even line between the top and bottom color. The white markings should be a pure clean white.