Back when I had access to a 4-gas exhaust analyzer and a voltage converter that allowed me to use it on road tests, (Thank you, public school system!) I was able to confirm that reading plug color was a very poor way to evaluate fuel mixture. One thing for sure- - - - -if a plug is black and sooty, you're not running rich- - - -it's more like REALLY RICH! An insulator that's blistered, or glassy-looking is a sign of a VERY lean condition. Anything in between is difficult to evaluate.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!