Quote Originally Posted by Flagg
I've got american blues and dumbos, haven;t yet produced a blue dumbo but produced plenty of blues and dumbos and my blues seem just as healthy as any other rat. I've outcrossed the blue line a couple times, but producing blues doesn't take THAT much inbreeding, just one generation really.

I don't think there is anything inherent in blues that makes them less healthy. Some blue lines have probably been inbred excessively which might account for it.
You may not notice the issues if you are feeding off most of the blue stock (as opposed to letting them grow up and die of old age). The issue comes in that ALL (I know it is a loaded word but essentially true in the grand scheme) blues are imbred. The original blue stock was only 1 rat found at a pet store in California (a blue hooded if memory serves). A few more were imported from Europe (and elsewhere) but no where near enough to forestall tons of imbreeding. So though you are outcrossing more than likely the blues are related somewhere in their near genetic pasts which is turn washes out the genes. There is just not a strong gene pool for blues in the US - and unfortunatley the pool that exists is weak and prone to issues (those that Becky points out).