My experience with pumping, and one I’ve heard expressed from other veterans, is if a session is effective there is some degree of ongoing increased blood flow for a a good while. This results in the penis being darker and warmer than normal for several hours. So some of the transient discoloration might be a positive indicator.
Also, I do seem to get some transient increase shaft skin color where it doesn’t pack the tube, and a little discoloration (but less) where it takes some time to pack. This usually resolves or mostly resolves within 24-48 hours or so. It is a different kind of discoloration that remains after the more reddish, heat-related discoloration, and it seems tough to avoid if the session is anywhere near valuable, at least for growth-level pressure.
Petechiae are another issue, though, and those take a few days to resolve and are much more unsightly, so I try to avoid them.
A few things seem to help prevent them, other than conditioning and good session technique: make sure you aren’t taking anything that affects platelet function, like aspirin, ibuprofen or other NSAIDs. Some supplements, like fish oil or EFA’s can also affect clotting, so know what you are taking and plan accordingly. If you are taking NSAID’s, give yourself a few days off of them (7-10 days for aspirin and 3 or 4 on any other kind) and you will be surprised how much more pressure you can use and not get petechiae.
I started taking a supplemental enzyme called serrapeptase, as it is reportedly good for inflammation and as an added benefit, might help prevent or even reverse atherosclerosis. Turns out it helps dissolve clots a bit, and I’ve found bruising and petechiae resolve much faster since I’ve been on it. Like 24 hours as opposed to 3 or 4 days. So it might be worth looking into.
Finally, arnica creams do seem to help resolve things more quickly, too, so I use that if I’ve overdone it a bit.