Supertrapp FAQ - Spark Plug coloring
Coffee with light cream = Just right.
Dark = Too rich. You need to add discs.

Seems straightforward enough.

So, what's it called when the exhaust diffusers have two color tones? I'm thinking it was long term exposure to jetting that was too rich for a period and since adjusted via AEM UEGO lambda readings to 'Just right." Power and throttle response are the best they've ever been, so I'm thinking the diffusers are going through an evolution.

Thought I'd share, just for the pure curiosity of it.