the tale of the spark plug

The experts say every spark plug tells a story: Dry and light brown = lean, Dark and wet = rich.

I went down to Hot Shots yesterday and couldn't get the bike started again. I pulled the spark plug and the photo above tells the story. Half of it is clean and new, the other half is dark and wet. If only I could understand the nuances of the language. What does it all mean? I think it is an existential question...