Why are albino domestic rats relatively common

When most albinos are rare even in captivity.I own three albinos at least I guess you would call them albinos white fur red eyes pink ears and tail.Albino mice are also common so why is this.

Every Albino is a Pink Eyed White, but not every Pink Eyed white is an Albino. You can only prove that you have Albino with genetic testing.

Note, I went and did some more research on the web and came back to edit my answer. Seems like I'm learning too from your question.

From the website:

http://ratguide.com/breeding/genetics/ap...

"...a white rat that is genetically an albino may look just like a pink eyed white rat that is not albino, but whose color has been faded out from dilutions. Although they both have the same genotype (pink eyed white) they have very different genotypes (genetic makeup)."

This breeder knows that this rat is an Albino because she knows the genetic makeup of her rat

http://www.spoiledratten.com/breedingrat...

The pet market is saturated with PEWs/Albino rats. The Rat Fancy calls them Pink Eyed White when we can't prove that they are Albino. If you breed pure Albino to pure Albino you get all Albino in the litter. Pet stores have a tendency to let their rats randomly breed, so a cage full of PEWs may or may not be pure. If they both look like PEW, but they carry other genetic material they will produce both PEW and colored babies. If a PEW is bred with any other colored rat, there will still be some PEWs in the litter. That's why they are so common.