I replaced my spark plugs at 45,000km a couple of weeks ago...
I know it's not needed as the Iridiums have a service life of around 100,000k - but I got them at a 20% off sale ages ago at a cost of around $8 a pop, so no biggie.
The brown ring on the ceramic insulator is "normal" to an extent, tho i'm not sure it should be that much on 45,000kms

You can see the firing electrode tip end looks fairly clean, a small amount of deposit on it. The needle tip looked fine also the flat bit had some deposit but a groove indicating that any spark would have "contact" between the needle point and the metal conductor.
You can see some of the deposits falling off from the 2nd spark plug in the last two photos...



