Hiya , this is completely normal he/she is just growing into their adult fur here’s a pic of my grey rat when I bought him and now ... as u can see he was VERY dark ... almost a black colour but now he is very light almost white Colour
Thanks for replying This made me feel a lot calmer.
I don’t believe it is all gray rats but rather specifically roans that get lighter with age (there may be others but in this case, it is due to the roan gene).So grey rats will 'grey out' as the grow up, like a grey horse? That's interesting!
I almost said roan, so funny. I know gray horses don't start gray. My Arabian was born a dun, and by 3 started going gray. Turned rose dapple by 10, turned flea-bitten gray by 15 and was nearly white by 18.
Rastbian is correct, your rat is a roan and it will lighten with age.