I was reading a post about how to replace spark plugs the other day so I decided to pull them just to check them out. The bottom of the plug looked fine but the top (white ceramic) part that is outside the combustion chamber had some discoloration. Almost looked like they had been overheated and were brown in color about 1/4 the way up the ceramic part. I am running the stock NGK plug.

Should I consider replacing the plugs or is this a normal occurence? I've searched for spark plug threads to no avail.

 

Slight discoloration of the ceramic insulator is normal. Take a look at this page, it as examples of what spark plugs should look like after use.
http://www.dansmc.com/Spark_Plugs/Spark_Pl...gs_catalog.html

 

A bit of brown on the plug insulator is from oil that gets baked onto the surface of the ceramic. Somewhere, a tiny bit of oil is escaping into the plug cavity. When the plug operates it gets a charge which attracts any oil in the local air. It does no harm. It would go away if no more oil got into the area. If it's not extreme and it seems dry in the cavity, I'd do nothing except noting it on the records.

Stan