The tip of the insulator's color indicates only if you are using the correct heat range. You need to look way down inside the plug at the junction between the insulator and the body of the plug. How far up the insulator the carbon ring extends indicates how rich it is. And if you are checking full throttle mixture, the only accurate way is to put in new plugs, do a WOT pull, and before you let off the gas, kill the ignition. Then pull off the road and pull your plugs and look at them. Otherwise, if you do a pull, then cruise, then idle, then shut it off, what you will be looking at is the idle mixture.
foggy's "spark plug analysis" even states right at the top that it is a heat range analysis.
I'm not sure that going purely by color for heat range analysis is accurate with today's fuel.
But as far as mixture goes, what I described still holds true. Haven't you ever wondered what those mechanics at the track were looking at with their lighted magnifying glasses in the spark plugs?