Megacolon visual?

Ok, so I have been told you can tell if a rat has megacolon by the markings on their back. I have seen every popular pet store (Petsmart, Petco) carry their "fancy" rats with black or brown masks and stripes down their backs.

Is this true?

No, this is not true. Stripes down their backs have absolutely nothing to do with megacolon.. it is generally said that a rat who may have megacolon or may carry it genetically carries a blaze pattern on their heads.. when I was breeding fancies for the pet trade, it is the blazed pattern rats I and others quit working with due to the high occurance of megacolon. Megacolon is linked to high white colors.

http://www.afrma.org/megacecum.htm

Certain lines of high whites and American Blues are prone to megacolon, but there are no visual indicators. The only sure way to find if your line carries megacolon or not is to inbred (daughter x father, mother x son, brother x sister).

If you like high whites but don't want to go through a lot of trouble to find out if your line is 'clean' or not, I'd just breed the high whites to self (solid) colored rats. It will greatly reduce the chance of megacolon and you will still (likely) throw high whites.