[trularin]

My plugs foul when the engine is cold as the choke dumps fuel in to keep it running. After it idels down and gets warm, the choke opens and the engienn leans way out. If you pull your plugs in the winter from an engine that is not allowed to reach temp, you may get the wrong impression and start trying to fix it.

A nice medium brown color is ideal. You also will want to note if the electrode is "worn". Ernie has some good info there and should put you in a direction.