Most remote wires on aftermarket headunits are light blue.
To be sure, check the wire with a multi-meter after the headunit is wired up correctly and powered on. Touch the pos (+) end of the multi-meter to the wire and the neg (-) lead to a good chassis ground. There should be 12v.
Turn the ignition off, or turn the headunit off. The 12v source should go away.
Hope this helps.