I have an uphill stretch of road behind my house that I can pin the throttle WOT and ride a mile or so to my house when I test jetting. The best way is to WOT, chop the throttle, kill the engine with the kill switch and then remove the plugs right there for the most accurate reading.
Based on my testing on a 4 stroke dual purpose bike, you are looking for a grey color on the base ring (yes, the flat area that the electrode is welded to). The trick is to get as close to a grey color w/o going too lean (white) and melting the electrode.
For street applications (as opposed to race conditions) you want to stay on a bit richer side than at optimum, so based on your pictures, you're getting pretty close.
Signs that you are getting close to a
too lean condition are very small aluminum balls (sometimes almost microscopic) on the electrode. If you get that, you know you're a step to lean and need to back off (go richer) the mains one step.
That's to isolate the mains. From there, you start playing with the needle clip position/s and finally the mixture screws settings. Remember, if you change the main jets, the other settings can change, so it's always better to select the main jets first and work your way down to the mixture screw settings.
Also, you should check the carb sync when you get to the mixture screw settings.