I have had some like that in the past, and actually have two right now...thing is, mine have all had curly whiskers. The two that I have right now are still very tiny (born maybe 2 weeks ago), but I had two other males that I let grow...they grew out of the exact same coat you're talking about, and they looked just like normal rats with maybe a tiny bit thinner fur. Nobody else noticed this, nobody even remember the texture and look of their coat as babies, they looked so normal and fit in so well with the bigger boys. They were snake food, and are long gone, now, or else I would gladly take a better look at them.

If you're going to let yours grow, please do keep us all updated as to how it comes along. If I remember, I'll also let you know what goes on with my two as they get older. I am keeping both, because they are solid blacks and I don't get many solids in my litters (i do, however, get a bunch of other black combos), so I'll get to see them progress through their whole lives.