They could be caused by one of three genes - you won't find out which til later on. That gives six possibilities as to colour since one parent is agouti based and the other is non-agouti ... the eyes will probably be your best indicator.
1. Red eye dilute: Misleadingly named, if they grow to have dark ruby, almost black eyes, then they'll be caused by this gene. An agouti based RED rat (A-rr) is topaz - this is a ticked warm golden colour, with white guard hairs, and a blue undercoat. A non-agouti based RED rat (aarr) is buff - this is a warm, mushroom magnolia colour all over.
2. Pink eye dilute: Not so misleadingly named! Bright pink eyes, like an albino. An agouti based PED rat is a silver fawn - this is a ticked bright orange, white guard hairs, and no real undercoat colour. The non-agouti version is champagne, which can be quite similar to beige (usually paler), and of course those brilliant pink eyes.
3. Himalayan: In your kittens this would be expressing as Siamese (chch). This would have red eyes, not so pale as to be pink but not so dark they could be mistaken for black. You'd notice that the colour doesn't seem very even, maybe getting darker towards the tail, then at 5-6 weeks old they'd moult out to a very pale colour with slight markings at the nose and tailbase.
I would guess, if I had to, that they're most likely red eye dilute colours. The red eye dilute gene is really common in American rats, with the pink eye dilute gene being rarer (exactly the opposite situation in the UK). Time will tell though!
