Headphone wire color coding
Red is for Right. Blue (or green) is for Left. Copper is for ground (I remember this with the mnemonic Red Right bLue Left Copper Common). All 3 are coated in a lacquer you need to burn or scrape off before you solder.   With standard headphone plugs, with the plug facing away from you, the right pin is right, the center pin is ground, and the left pin is left. 


Common (or "ground")
Right
Left
Insulating ring