Grand Prix Wiring in door

Hi all.  I have a few questions about the speaker wire colors on a 2004 Grand Prix gt (non-Bose).  I am trying to run a 4 channel amp to the stock speakers.  In the left driver's door, the 5'' has a grey and brown wire.  Does anyone know which one is the positive/negitive?  Conversly, is there any way to tell a speakers polarity if it's not written on the terminals?  Also does anyone know where I can find the stock wire colors and their polarities?  Thanks!

You can pop the speakers for polarity.  This is described in detail in the sticky "how to figure out stereo wiring".  GM has used the same wire colors for years, so you can just look up another car to the left under "vehicle wiring".  For speakers I try to remember the lights as positive up front, and negative in the rear.My ex once told me I have a perfect face for radio.