I had a crank break in the exact same location #1 and the exact same way. It ran, just like yours and only made a slight knocking sound I heard one day in a parking garage. It was on my wife's escort though, not a GN.
I think that that portion of the crank gets loaded some from the accessories on the front of the car, the front main bearing reacts the up and down load, but there is some bending that reaches that portion of the crank. That's why at the crack, you can see in the picture what looks like a 1/8" gap there. I bet, like mine the #1 bearing is torn up really well now and probably now if you remove all accessories you can move the broken snout of the crank up and down pretty well. Once cracked as that crank rotates, those surfaces rub relative to each other just like you see when you pull up and down on the detached end. I'm guessing that maybe the heat from the friction of these surface rubbing together has caused the discolorization you see. The portion towards the rod has much less material and would probably get a bit hotter. It's tough to see but I think there is a litte discolored area on the other beefie side as well. Just a guess.
In my case, I never found what was wrong for sure. I just put another crank and bearings in it, cleaned everything, put it together and drove it for a few years and maybe another 30k miles or so. The motor always ran like new after that. I never did allign hone the block, and the new crank rotated as it should, and all clearances checked OK ( for an escort of course). I have a feeling if there is excessive clearance in the #1 bearing it will load up that area of the crank and that extra clearance will contribute to cracks in that area. The problem is you can't really check it very well because that journal and bearing is destroyed when the crank snaps.