Does anyone know what all the stereo wire colors represent
 

Yes, I am too cheap to buy a harness adapter ;)

There is a big yellow wire - I am guessing that must be the 12v power.

Does anyone have a list of what each color wire goes to?

Buy the harness...i tried it & I'm quite nifty with the wiring game...I broke down and said screw it!
But..you can try here:
http://web2.airmail.net/theman/protegefaq/
Welcome to the site also!
-Phil

Yellow is accesory power, red is constant, black is ground, purple is right rear, green is left rear, gray is right front, white is left front. That's all from memory, but I think it's right.

Pin #: Wire Color - Use

Pin 1: Green / Orange - Rear Right Speaker (-)
Pin 2: Green - Rear Right Speaker (+)
Pin 3: Brown - Rear Left Speaker (-)
Pin 4: Brown / White - Rear Left Speaker (+)
Pin 5: White - Front Right (-)
Pin 6: Red - Front Right (+)
Pin 7: Black / White - Front left (-)
Pin 8: Black / Brown - Front Left (+)
Pin 9: Black - Ground
Pin 10: Pink / Black - Switched power, coonect to red wire in aftermarket harness.
Pin 11: White / Blue - Dimmer, not typicaly used for an aftermarket radio
Pin 12: Green / Black - Illumination, thanks twizyours
Pin 13: Blue / Red - Contasnt Power aka Battery aka Memory, connect to yellow wire in aftermarket harness.

but really, just buy a harness.

Oh, and anarchist, Yellowis constant, red is switched.