Nars concealer!
Very strange - I've had a bit of the dreaded P on my forearms - a real stubborn little patch - and I've been using my Nars concealer to tone it down so that I can wear short sleeved tops (the concealer is quite good for covering a little plaque.
Most strange, but after a couple of weeks of doing this, the patch has cleared up. It's been there for about six months - nothing too big, but a little annoying for wearing T-shirts.
Not sure if it has anything to do with the concealer - or just the fact that once it was concealed I didn't think about it - but it is most strange.
Have also found Benefit concealer good in the past for hiding P on my arms - but it never cleared it away.