Doesnt Matter for a link, but generally as you said, same colour to each other, If you use Black and red wire also then it is far easier to fault find knowing that all the black wires & connectors are negaitve and all the Red ones are Positive. If you use Drill Motors you might have noticed that one terminal has a red mark or dimple next to it, Most Manufactures use this to indicate that it is the Positive motor connetion where the motor will turn Clockwise, I also use red wires for this and black for the other (Where possible) , Knowing this Eliminates the guess work on which way the motor will run when wired up. For example in most robots the motors are opposite each other so you then know that if you connect one motor to the speed controller the other way around (ie Red to negative on the speed controller, and black to positive) then the wheels will go the same way around, assuming you get the receiver connections in the correct channels as well.