i neighter have relly understood why som manufacturens use diffrent collour on the wires, but each wire is just the sameonly thing i could think of that will be diffrent is the lenght of the wires.
The reason for the colour coding is to distinguish what wire is for what and also to help to reduce the chances of mistakes when they are assembled.
like so http://en.wikipedia.org/wiki/Power_supply_unit_(computer)#Wiring_diagrams