It took a year for my heavily discoloured penis shaft to return back to its natural skin colour. I was experimenting with a special hanging pump which caused the discoloration to reach half way down my shaft, it looked odd and unnatural.
I tried
Amlactin lotion which was recommended by some Thunder's place members, it's supposed to speed up the replacement of skin cells but it didn't help much.
Others have tried an acid peel to speed things up but suffered a lot.
The only thing you can do is stop pumping and wait a year, you can continue PE with other methods instead.
To avoid discolouration is a better solution, I find the blood spotting (that causes it) appears if you pump at a high vacuum for too long, I found that it usually occured above 4 Hg of vacuum after 10 minutes. If it does occur, immediately wash and dry your cock then apply a generous amount of arnica gel, several times after your session. Have a day or two off until the redness disappears.