Hello there Andy.
Re-telling one of my favourite stories, but the body and your skin in particular, does have a surprisingly effective "re-tightening" mechanism of which a good example is the lax skin that many women have immediately after the birth of a baby, but which does actually tend to "take up the slack" over a period of some months. And the same thing happens with people who lose large amounts of weight by aggressive diet control (including gastric banding procedures).
Sometimes even the breasts "tighten up" a little after weight loss, though in that case, there is something working against it - the continued pull of gravity on the remaining bulk.
So in your case, we do not find this entirely surprising - you probably
will need to do some more stretching, and you no doubt
will need to continue it for longer after you achieve the "desired" point of function, and it may well appear at this stage, that the skin has "toughened" up a little, as it may have appeared before you started the stretching, because the "growth" to which Jim commonly refers, as a result of the stretching has not continued to be directed in the "stretching" direction.
The main point remains, not to become discouraged with the process - the fraenulum clearly is a rather finickity piece to stretch - it is
difficult to be sure, but equally
do-able and I hope you will agree, the method is easier than many others.
As to the colouration of your median raphe, that is a little curious. While it would not particularly surprise me if the stretching process caused some pigmentation of the skin that was undergoing stretching, clearly the remainder of your penis skin is
not being stretched, and this would have no connection at all with the stretching process - and bruising is pretty unlikely. If you were to take a look at the area around your anus with a mirror, I suspect you may find this also to be pigmented, because it tends to "chafe" from rubbing together, and the pigmentation - if you are prone to it - is a result.
The usual causes of this pigmentation, apart form being vastly more prominent in darker-skinned people, are hormonal, notably (the first) pregnancy in women. That is clearly not relevant to yourself; there are others related to adrenal gland malfunction, but I really would not advise concern about these if you are otherwise perfectly healthy.
I'd put it down to a novelty (and suspect it
was actually there before

), and suggest you just keep on with the stretching.