After years of stopping girth work, the discoloration has faded away for me. I applied Tamanu oil everyday, but I can't say if it was the oil or just time.
I have also used micro needling to resolve some discoloration immediately after it occurred, i.e. i got some discoloration from pumping and that night i used a 1.5mm micro needle stamp. Before using the stamp i wiped my shaft down with an alcohol swab and after i was done i moisturized with a hyaluronic acid cream.. But i don't know how effective it is for long term discoloration, and it does hurt and make your penis bloody.