All pads get dirty. All pads can be cleaned if they're not stained. Stains don't generally come out of leather, so if you're thinking about the white Roos, I suggest not drinking anything dark while you're playing, because it will show particularly well against white, and will also show on "natural" brown leather -- just not quite so obviously.
BTW, even so, the only person likely to notice will be you. You really do need to be close to the horn to notice.
All leather pads will get dirty, be they kidskin or roo or whatever. Roo is a denser leather than kid with finer follicles, so it tends not to absorb the dirt and gunk so much as kidskin. In any case, you can clean your pads if you're that worried.
The most effective method I have found to clean soiled white roos is a soft white art eraser. Swabbing the sax after every time it is played will go a long way to keeping the pads clean, no matter what the color or type of leather.
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