Spark plugs from a properly tuned engine will be clean and white but without microscopic pepper specks.

Reading a spark plug for the optimum main jet size and power is another one of those interned topics where the want to be tuners are  grossly misleading the new comers to the motor sports world. 

A spark plug is not a sensor for air fuel ratio, a spark plug is not a dyno or performance measuring device.  A spark plug is just a device that sparks and ignites the mixture. 

The only accurate conclusion we can come to when looking at a spark plug is whether the various parts of a spark plug were operating in it's optimum temperature range

A spark plug must operate at a temperature that is hot enough that it keeps deposits burned off the porcelain cone that surrounds the center electrode, but not at a high enough temperature that the hot spark plug ignites the mixture before it sparks (this is what is called pre-ignition.  This temperature range is only about 500 deg.F wide.  When the plug temp. is too low, carbon deposits are not burned off and the plug fouls. 

I can make spark look black and on the verge of fouling when it has jetting lean enough that power has dropped below max power and the exhaust temperature is high enough to burn the exhaust side of the piston.  This can be done when the heat range of the spark plug is too cold and or the coolant temperature is too cold and or the time one spends at full throttle is very brief. 

I can make a spark look white and on the verge of causing pre-ignition when it has jetting rich enough so that the engine is rich misfiring.  This can be done when the heat range of the spark plug is too hot and or the coolant temperature is too hot and or the time one spends at full throttle is excessively long. 

Tune the engine so that it has a slight rich misfire and lean the various circuits so that it just runs clean while monitoring the spark plug for traces for detonation.  Engines tuned with the method will be reliable and will produce very close to optimum power.  Once you have the engine tuned using this method of tuning, install the heat range that produces a clean porcelain cone and does not have any detonation specks.

Tune the bike under the same conditions as it will be ridden.  Running the bike up and down the highway wide open and doing plug chops does not simulate riding the bike in the woods, dunes or race track.