Congratulations! It's always fun seeing recessives come out.

Inbreeding isn't too bad in rats, it just depends on what you have. If there are deleterious genes in the animals' bloodline, those may come out with inbreeding. Outcrossing won't make the traits go away, it will just take longer for them to come out, while also risking spreading them throughout the bloodline (so when they do come out, you won't know where to turn and may have to scrap the whole line if its a bad enough trait). With inbreeding you'll find out it's there, and can take appropriate action to breed away from it or get rid of it. Likewise if there are desirable genes (like the recessive coloration you are seeing in this litter), inbreeding can bring those genes out too, and you can select for them. Neither inbreeding, linebreeding, nor outcrossing are bad in and of themselves, they are just tools. What makes them good or bad depends on how you use them.