That grey is most likely exhaust gas. Restrictive exhaust or too much overlap?
To be honest in my opinion that second one is very good. What the spark plug tells you is the mixture AFR and quality of the mixture at time of ignition. Just because you give the cylinder a certain AFR doesn't mean that's what it is at the plug at time of ignition. Timing mark is myth.
Good to see people actually reading plugs instead of just an O2 gauge.
The fuel curve was surprisingly flat. After lots of carb changes we were able to get it to cruise (30-50% load 3500rpm) at around 12.9 and wot was flat, varying only a tenth or two afr points, 11.4- 11.6 from 3500-6100 where we shut it off.