Green spark plug electrode, others fine, causes?

I was changing the plugs in my car tonight and the last plug (clost to the firewall on the driver side) had a green tint to the electrode on the plug. All the others plugs were looking great, just a slight bownish tint to them. What could cause this one plug to differ from all the others, I'm pretty sure the green is signs to the plugs running hot? My mods are TFS TW heads, Ed Curtis cam, Edelbrock intake manifold, 24lb injectors, 80mm ProM MAF...the shortblock is stock and I had Autolite 3924 plugs in it. Any advice is greatly appreciate, thanks in advance.

Yea, but it's just the grounding strap I mean, not the electrode, and it's just the tip back, the porcelin is bright white. The rest of the plug looks good. I've heard that the copper in the spark plugs will turn green if they get too hot (lean).