Spark plug color is usually generated over a fixed throttle position, fixed load for an extended period of time then the engine is chopped or shut down rapidly, clutch in throttle shut, pull over, read plugs .That applied to carburetor engines and leaded fuels .With unleaded fuel and fuel injection there are data inputs that vary the fuel map even at steady state throttle conditions making plug reading ambiguous at best.
What the plugs can show is out of the ordinary or extremes in engine and running conditions, with the engine having been run at temp for an good period of time with the correct heat range plug a black sooty plug would indicate a rich fuel condition ,a blistered ground strap and insulator would indicate a leaner condition ,a wet oily black plug is usually engine damage as is an ash build up on the ground strap and insulator nose .fuel additives can also make residue on the plugs that mask a reading .A very light tan/grey white would be the most common color for a plug but that still is not an indication of an engine running at its all round best condition .The best value for money is getting your engine dyno tuned using advanced mapping ,this will give the best all round running and performance for your bike.
Also the old stories about tail pipe color only applied to leaded fuels, that lovely grey/white color that everyone strived for was pure tetra ethyl lead residue, not very nice stuff to have in your lungs and blood stream.

can you post a pic up of your plugs

here is another thread on the subject... the link to my photos was broken so Ive just reinstated...

www.hdforums.com.au/Default.aspx