More info please, so I can better answer your question.
Are your grey babies totally grey or do they have white bellies like mom and dad?
If they are a solid color are they a soft blue-grey or more of a washed out black?
Are you SURE you have a single litter of babies and not two? How great is that size difference? (Campbells can have a second litter 18 days after the first - so you could have two litters if there is a large size difference).
Do you know the actual date of delivery? The difference between 3 weeks and 4 weeks is a lot in hamster days.
EDIT - ok with the additional information I'm more confused - or I'm missing something obvious and will be kicking myself later for it.
I want to say you have Campbells dwarfs based on the colouring, but if the parents are both "orangey with red eyes and white bellies" it means they are one of the colours red eyed lilac, blue fawn, beige, or dark beige (not necessarily the same colour as each other) - no combination of those would give you a grey baby with black eyes and a white tummy (sounds like opal or agouti, but most folks would call an agouti brown rather than grey)
Dumb questions - are you sure that both mom and dad have red eyes? or did you maybe look at the same one twice on accident? how sure are you that these are the parents?
Anyone on here know Winter White genetics??? Would that make genetic sense for these? I know there is a sapphire colour that could easily be described as grey, but they only orangeish colour I can think of would be the one that turned out to be the hybrid (can't think of name - pudding? maybe) and I don't know the eye colour offhand.
As an FYI - "russian dwarf" is a misnomer and won't actually tell you what you have as different dwarf species are called by that name despite being different creatures. Folks incorrectly using the names and not really knowing what they own is the cause of some of the unfortunate hybrid incidents that have occured. The four types of dwarf hamsters available as pets are "Campbells", "Winter Whites" - both of these are what folks sometimes call russian - "Robovorski" and "Chinese".