I don't remember the red and green wire being constant 12V... Could be wrong though, it's been a while..
"Usually" there will be;
Solid yellow/orange which is constant 12V.
Red which is ACC
Black which is earth.
Any purples, greens, greys, brown ect it usually a speaker wire.
You should be able to tell which are speakers because there will be two wires the same colour, one of which will have a black stripe.
The black stripe wires neg to the speaker.
The U12 has plugs half way through the wire as well. At the headunit, there will be (hypothetical colours); 2 purple and 2 brown, but just before they exit the shell of the car and go into the doors will be a plug changing them to black. That's why at both doors there's a black and black and white wire...
Just a bit of FYI.. Like crimps, itl probably lose a bit of current there
If you have a test light, you should b able to figure out whatever you need.
Check the green and red isn't actually just a ACC wire..
Anyhoo, goodluck