I know the truly ideal way to read spark plugs is by cutting off the threads and examining the insulator, but I hope this picture shows enough information. I'm in the process of tuning my idle and I think I'm running a bit rich.

I started with a new set of ACDelco R43TS plugs and ran the engine at idle for about ten minutes each time. Between tests I cleaned the plugs with brake cleaner. The upper picture shows the first run with my original idle fuel calibration. I leaned the mixture out a bit via the EPROM, but for one reason or another, the MAF sensor was picking up more airflow and thus ran the engine in a richer state the second time around (lower picture). I think the two images demonstrate this, but I just want to be sure that I'm seeing a less-than-ideal situation here.

This is a new engine with less than 1000 miles, so the little bit of oil on the plugs appears normal. I have not run the engine at anything other than idle with these plugs.

 

from the pictures it looks to me like all but #4 are lean...

 

These plugs do not show a rich setting, if it was running rich the plugs would be black and sooty.
You really can't get a reading from idling, I would install them, do some driving and take some more photos and put 'em back on here.

 

Yeah, I'm starting to see that now... I guess the oily residue was confusing me. I knew I had a rich condition at idle and was expecting to see some more carbon. After some normal driving they looked alright. Guess I'll just have to use a wide-band O2 to really nail the idle mixture.