Ok, now I can lower my panic a bit. Every plug manufacture uses a different coating on the plug and they all read a bit differently.
Now the color change on the ground wire and the heat in the shell make sense!!!
I have an Autolite book coming and hopefully it will give some data on what changes in heat will do to the shell coating.
You have plenty of ignition and it sounds like you have the tune up pretty damn close which is why there isn't much color on the upper porcelain and that's not a bad thing.
I say you are damn close, I just want to see a fuel ring down in the bottom of the plug. That WOT but it will still develop over time even if you aren't at WOT. WOT pulls will just make the ring show up sooner.
The ring should be .060-.080 wide, maybe .100 depending on what the engine wants.