Those are some very high white genes you're using.. Yes, they may be pretty, but that would not be something I, or alot of other people, would use for producing feeders.

The male is either a russian blue or dark american blue possum dalmation... NOT a safe marking to be working with if they came from a pet store or unpedigreed lines.

The female is a lightning blaze with a bit of variegation on her sides.

www.ratguide.com

I honestly would not use those two or any others that are blazed/marked/high white in your colony. Why is it that everyone is very willing to risk using these marked rats UNTIL they get a megacolon litter? Why not just prevent it altogether?

Megacolon can sometimes show up at 3-4 weeks, sometimes at 6-8 weeks, and sometimes even at 6 months or after. Have you kept babies past 6 months to ensure they don't have problems?