Spark plug pics, what's this coloring mean?

These came out of my '96 XJ 4.0. Plugs from cylinders 2-6 all looked like the plug on he left, barely to somewhat tanned, normal. But the plug from cylinder 1 is on the right and it obviously has something going on. The plug threads are significantly darker than the others and on the plug ceramic the coloration is much darker all the way around except on the side where the electrode extends out of the plug where there's no coloration at all. Whatever this is it's happening in cylinder 1 all the way at the front of the motor.







Motor has 150k on it.

Anyone have an idea of what's going on here? Thanks.

Unburned fuel. Plug isn't getting enough of a spark - or it is just getting over-fueled. Bad wires? Bad plug?

It looks like a shot/leaky intake valve guide.

Forgot to mention, these came out during a complete tuneup using all mopar parts from the coil to the plugs. Motor had a miss before and runs better afterwards but still has somewhat of a miss. I was wondering if it was maybe a bad motor mount (I think a bad motor mount can mimic a miss?).

The darkened area has no kind of gunk build up. It's exactly like the other plug far as surface condition goes, just with the dark coloring. There doesn't appear to be any oil residue.

I've had suggested that the plug was facing a bad valve thus the pattern coloring. I'll have to say the coloring is so symmetrically aligned with the electrode that the chance of the plug's electrode and valve lining up that exactly is smaller than the chance that whatever's causing this to happen, the pattern is more likely to be showing up as a function of it's relationship to the electrode.

carbon.
Oil in the cylinder
too much fuel
weak spark.

you're not burning everything that's in that cylinder.

Check compression. #1 might be low.