It almost sounds like there is some quality to the darker skin that repels the product more than lighter skin (moisture, stratum depth?). I think I’d be tempted to experiment with various substances (alcohol, oils/grease, H2O2 etc) in selected areas of normal skin to see if one or more of them is capable of creating a surrounding barrier to make the stuff to stay in place, without unduly forcing already good skin to recycle.
I’m done for now. There are still some very faint small darker patches on the left side. They aren’t noticeable enough to worry about. I’m sure the circ scar will fill in as before after some PE, and the shaft will darken again to some degree.
I wish I had pictures. The improvement has been dramatic. Before, my darkening was similar to dano1122’s.