How can I know for sure if my cat has fleas?

I have 2 cats- both indoor cats that NEVER go out.
Recently one of them has been scratching a LOT and excessively grooming himself.
The thing is- he is almost all white- and I have checked his fur and brushed him etc- and have not seen a flea or anything like that. I figure on this white coat they would be easy to spot, no?
Also they have never gone outside- so I would imagine fleas would be hard to get- unless they jumped through a window screen?

I am assuming that he might have a skin allergy or something- but before I take him to the vet - is there any sure fire way to look for fleas?

Re: How can I know for sure if my cat has fleas?

You would see a live flea walking or flea dirt, which will look like black pepper sprinkled on the tummy/groin area for sure.