Although not recognised as a variety in its own right for showing in the UK, masked is used as a term for a fairly common mismark that can be seen in litters when breeding for black eyed white or capped rats.
Genetics: As for capped (homozygous for notched or extreme hooded locus – hnhn, hehe – presumably hehn), but selected for more white markings.
AFRMA standard: Masked rats may be shown in any recognized color. The body is to be a pure, clean white, free from spots or brindling. A colored mask to cover the face, to include just around the eyes and above the nose, not to extend down the sides of the face onto the jowls or under the chin.