I used to get bad discoloration too, especially during the first half of year into Penis Enlargement. My penis had this dark, "dirty"-looking "band" around the shaft, mostly on the underbelly of my shaft. Even my (then)girlfriend noticed.
Don't freak out about it. It goes away. I've been doing Penis Enlargement for a little over a year now, and I don't notice it that much anymore. Maybe I'm used to it now, but I think most of it cleared up on it's own, really.
It'll show more when I'm flaccid, but erect, it's hardly there.
I've found that Uli-type exercises helped dissipate the discoloration. Of course, with the girth workout I do, temporary discoloration is a given. My cock is always a little redder than normal, but it's for good cause. And, if I take some time off of those, that discoloration will go away too.