Finally an item where we don't have to be high tech.
The best way to clean whitewall tires is simply to use a lot of water, dab the whitewalls with a soft brush / sponge with green soap, let it soak in so that dirt and grease have a chance to soak well, the white lines are good again scrub and then rinse away the soap and dirt residues with a hose or high-pressure cleaner.
Dry your tires and you're done. It is also important to clean the whitewalls regularly, so that the dirt does not corrode. Doing this every other week is no exaggeration. The use of abrasives and aggressive cleaning agents, eg chlorine, is strongly discouraged, as these products can damage the white wall.
This cleaning method also applies to the first cleaning of new white wall tires where 'the white' is protected by a colored protective layer.
Oh yes: of course there are also smart, specially developed products on the market for cleaning whitewalls. Feel free!