Interesting look. Strap looks great to me but the carbon around the threads looks like you are a little rich at times. Maybe the idle is rich?

If I had to take an educated guess I would say you have a rich idle but the mixture above idle looks pretty good.

Sometimes photos can lose/gain color and I can't see the condition of the center or ground electrodes but that is my read on it.

Are you experiencing any drivability problems or just looking at the plugs?