Most rat colours are either ticked, shaded, or self – the pearl lies alone in being a tipped variety. Each hair on a pearl rat is tipped with the tiniest amount of mink, rather than being banded like a ticked rat is, or sound to the root as in a self.
The pearl gene can have a very variable effect on rats. The darkest phase pearl rats have only the tiniest amount of white undercoat, and look indistinguishable from minks until you part the fur. At the palest end, some rats are so extremely pearl that they have no tipping at all, just creamy white colour right to the end of the fur.
Genetics: Mink with one copy of the pearl gene (aammPepe). A very similar colour can be made using the American mink gene, though it’s not known whether it’s the same pearl gene or not (aaamamPelpel).
NFRS standard: To be palest silver, shading to creamish undercolour. Each hair to be delicately tipped with grey evenly over the whole animal. Belly fur to be creamy silver. Foot colour to match top. Eyes black.