Looks like it might be running rich to me. Does the exhaust have a fuel smell? Unless the plugs have some unusual heat range, I'd say too much fuel.

I would go for a cruise, shut off the engine right as you take your foot off the gas, and coast into your driveway. Don't let it idle. Try to be going 20 mph or more right before you shut it down. Then check the plugs and compare.

I'm guessing the engine was idleing for a little bit before you last turned off the engine.