Dark glans of vachanger

I have hanged with the vachanger for about a week, I have noticed that right after I take of the hanger after about 15mins of hanging the glans of the penis is dark on some parts, mainly at the front. It disappears after about 5-10 seconds and faster if I massage it but is this alright? I’m a bit worried. I may think the dark area is for pressing against the wall of the hanger during the hang but I’m not sure. Any comments?