PEWs, black rats, and siamaese/himis are the most common rats in rescue. That's like telling a dog rescue that dogs are very adoptable, except for labs, goldens, and GSDs.
In the past 3 years we've only had a few rats that weren't PEWs, black, or siamese. They were fawn hoods and one of the four got adopted.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry