Unfortunately I cdn’t find much info on this online, but I think what you’re describing is somewhat normal. I was circumcised at birth & the head (& approx. 1/3 of the end farthest from the base)is slightly lighter in color, the other area does become darker (reddish to almost purple) with extended stimulation, so I don’t think what you’re describing is really ‘abnormal’. Remember, everyone’s a little different, penises vary quite a bit in size, shape, etc., so I don’t think you have anything to worry about.
Also, I imagine that over time things will tend to normalize a bit. But even someone like me, circumcised at birth, can see differences from where the foreskin was cut. It never bothered me in the least. If this really concerns you that much, you should just see a Dr or Urologist, they could answer any questions about this & I’m pretty sure they’d reassure you that evthg’s OK. I know you said you’d rather not talk to a Dr., but if you just said, hey Doc, I was circumcised a cpl yrs ago & was just wondering, does this look like it’s healing OK & would I expect to see any additional changes in color, etc.? I think they would find this a pretty normal & non-embarrassing question. It would be pretty normal for any guy who had this type of procedure to wonder if things are looking the way they should.