The colour of plugs when you take them out.

[Steve Jones]

If you weaken the mixture, the car runs less well. If you richen the mixture the car runs less well. Perhaps that engine is trying hard to tell you something and that something is 'leave me alone'!! The object of the exercise is to get a car that runs well. The colour of the plug electrodes is of minor/no significance as long as that is achieved.

Steve