Spark plugs are white

I posted a week or so ago about a problem with overheating and a rough running 4.0L in my 96xj. Yesterday I pulled three spark plugs to take a look. They all appeared to be very white in color. They are regular champions from Napa. I have since diagnosed my overheating problem (bad aux fan relay). Did I possibly "cook" my plugs??? My xj just doesn't idle quite right. I also noticed too that one of the plugs had a carbon spot on the cermanic electrode insulator (inside combustion chamber) it was in line with the end of where the threads on the spark plug end...hope that description makes sense.

An ultra white plug means the plug is too hot. Especially if it has shiny spots on it. Dunno about the carbon spot. Try running a cooler plug.

you could also have coolant leaking into the combustion chamber. That'll kepp your plugs lookin nice and white.

White tends to mean running hot combustion temps. Normally caused by running too lean. If all plugs are the same then

Possible causes:
Bad Map
Bad O2
Leaky Brake Booster
Leak under Throttle body

If one or only some, then possible intake gasket leak.