One of Mooch's paws that was formerly all white I've noticed looks 'dirty' now on the bottom. I thought I'd heard that that can happen with white cats. Is there anything I can do to 'clean' it or is it just gonna be that way, kinda dingy?
Ollie's feet get dingy/ashy looking from litter digging... they clear up with his monthly bath though - maybe you could try just a little dawn soap on a wet wash cloth and then wipe it clean with another wet wash cloth and see if it's back to all sparkly white
I showed white cats (rexes) and use Nexxus Simply Silver shampoo which makes the white really white.
It can be used on any cat that has white (great for black/white too). Since you are talking paws only, it would be easy to just wash them and not the entire cat. But use it about once/twice a week till they are sparkle white again.
However, if the cat goes outside, you won't be able to keep them white white. And careful what kind of litter you are using - some leaves white with a dingy look.