+1 The black can be scrubbed off.Should a black sidewall tire have been severely scuffed against a curb, the underlying white rubber would be revealed; it is in a similar manner that raised white letter (RWL) tires are made.
That works on auto tires with white letters or narrow white walls because there is white rubber under the black. It does not work on motorcycle tires because there is no white rubber there to be exposed.+1 The black can be scrubbed off.
My buddy scrubbed his big 4X4 tires with some kind of common household scrub pad, but not sure what.
At my age, I'm not going to get down on my knees to clean whitewalls. And they DO take maintenance.