For single color, you just need a switched 12 volt 2 conductor independent of the speaker leads. 18ga is more that plenty. Controller is not needed for single color, just switch, but it can be used.
I have to buy a bunch of it for the speakers and some Oznium Superflux LEDs. Those are pretty small wires. I have to look on their web site, but I recall each LED being something like 80mA each.