so... I don't get it.... he's invisible, but his balls and part of his dick are double-darkness? is this like one of those 'seperate object' polygon rendering problems?
Probably, it seems to me than anyone going through the trouble of doing the invisible man thing is just trying to show penetration and it's easier to do that if you can tell where the bals are... but yeah he's prbably just trying to match the polygon deal.
It's like in some hentai games when you see something like this, the player would rather see everything happening so the player makes the raper get a transpent look so you can see in detail the rape XD