Hi. Are they rough to the touch, or smooth as the rest of the paw pads? Any sensitivity when touched? Any swelling that you can tell of? Is he indoor/outdoor? Any other similar blotches on his skin elsewhere? More information could help!!
This could easily be normal pigmentation. Hek has bi-colored toe beans. If the colored areas feel normal, no dryness, no thickening, no cracking, that's probably what it is. If the discolored skin does not feel normal, you should have your vet take a look.