What does "spark plugs appear yellow at the ignition point" mean? I was reading the DLE-120 engine User Manual and saw this paragraph:

Caution: Running the engine with a lean fuel mixture will cause the engine to overheat and burn the electrode of the spark plugs. Pay close attention to the High-speed Needle adjustment. Running the engine with the proper fuel mixture will make the spark plugs appear yellow at the ignition point.

What does &quot;yellow&quot; mean in &quot;Running the engine with the proper fuel mixture will make the spark plugs appear yellow at the ignition point&quot;?
Does anybody have any experience or images of this phenomenon?
Use the tip residue to evaluate the combustion process
The yellow the manual is describing is the normal condition found in the top left corner:

If the plug is not the yellow/tan shown in the top left, then it will almost certainly look like one of the other pictures. This is a strong hint that what is going on inside the cylinder is not optimal, and points in the direction of the problem.