Odd Spark Plug discoloration

[hop along]

Okay, shoot: see the brown discoloration in the insulation part of the spark plug, where it meets the metal?

What would cause this?  This photo was taken with only about 5,000 miles on the plugs, about 105,000 miles on the engine. 
FWIW this photo was also taken at time of replacement of the Cam Chain Tensioners (after the front failed). 
This plug was (still is) in the front left cylinder as you are sitting on the bike. 

Hop Along

[lragan]

As I recall, I already offered my (unsolicited and largely uninformed!) opinion on this phenomenon on the original thread regarding cam chain tensioners.  I don't recall anyone commenting one way or the other.

Perhaps my fellow MOOT members have concluded that the best response to an uninformed idiot is to ignore him!!

[Lurkin]

Not sure what Lawrence posted and too lazy to look it up, but I consider that line to just be the dirt/crud/rust that forms between the plug boot and the plug base.  Only time I would consider it an issue is if the plug sits in a "well" that is supposed to be covered from the elements, as in most newer car/truck engines where the plug is centrally located in the chamber and has a tube that gets it there.

[NWDub]

it's rust from exposure and that's where the boot ends.

happens to a lot of plugs that see the elements.

dielectric grease helps prevent it but it's not harmful for the most part.

[hop along]

It is in a 3rd gen Magna.  And by 5,000 miles, I also mean, it's only been in since the early part of this summer... in Oklahoma...
so rust as a possibility that never entered my mind.

Lawrence, I did see your comment in the other thread, but my curiosity and lack of google-fu to find an internet based answer got the best of me so I reposted its own thread.

Thanks,
Hop Along