So its the ASII carb with the shallow bowl and flat metal cap? It does like to be jetted leaner.
Other than the plug does the bike show any signs or symptoms of running lean? Cutting out, running hot, pinging, surging as you back the throttle off? Its very possible its just a combination of your fuels and or premix that are giving grey readings.
What happens if you go really rich? Does the power get softer and fluffier as expected? If you put a 185 in it will it start to break up in the higher rpm? This will be more evident in lower gears under little load.
I found my 2010 model when stock didn't give very good plug readings due to an exceptionally large squish clearance. Once bringing it in tight and having the fuel ignite under the spark where it should be the colour is much better.
To top it off see if you can get a used and dirty old plug and run a plug chop. If its truly lean it will indeed burn any existing colouring off the plug and leave it looking very white again.
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