Changed plugs today and they were brown in color

[cottonpicker14]

About 500 miles ago I changed my plugs (AC Delco R42LTS, gapped at .35) on my stock TTA.
Since then, I have been running a combo of 93 and 104 octane for a 98 octane, using a turbo tweak chip programmed for the 98 and 18 lbs of boost.
I had a small miss which turned to be a bad wire, but when I checked my plugs today, all the plugs were brown. The porcelin, electrode, etc was a brown color, almost the color of rust.
Any ideas whey all the plugs with only 500 miles would turn brown ?
Thanks

 

[cottonpicker14]

Here are two photos of the plugs

http://img.villagephotos.com/p/2002-12/74500/DSCF0906.JPG

http://img.villagephotos.com/p/2002-12/74500/DSCF0910.JPG

 

[Grumpy]

you run octane booster ??

 

[cottonpicker14]

No octane booster. I have been running 93 octane and 104 Sunoco Race gas unleaded at a 50/50 ratio.
Erics chip is setup for 98 octane too.