First you said your (US) pump gas doesn't colour plugs and it must be an Australian fuel thing:
Clearly all those plugs in post #18 that are from US cars are running US pump Fuel magically show colour when you claimed they can't or won't
Now you want to claim that race fuels don't colour plugs either? You can't seem to keep up with you're own claims.
Try a lower octane pump fuel. The reason your plug is white on the porcelain is its LEAN AT TIME OF IGNITION AT THE SPARK PLUG! It doesn't matter what AFR you give the cylinder in total its the AFR AT THE SPARK PLUG THAT MATTERS. In your case it’s LEAN, even though the rest of the cylinder can be really rich. Just because your carb meters an AFR of 12.8 that doesn't mean that's what it is through out the cylinder.