The blue wire is for the "running" portion of the front signals. Your LED signals will not function as running lights, so the blue wire will be unused. The black wire is ground, almost always, which leaves the other color wire (brown, whatever) as the blinker power wire.
What I did was to leave the connectors completely alone on the bike side of things. I took the stock blinkers off and cut off their connectors, leaving me with those three wires. I wrapped the blue one in some electrical tape, as it was not going to be used. I then used Posi-Lock connectors to connect the black wire of the cut-off plug to the black wire of the LED signal, and the brown (or whatever) wire of the cut-off plug to the red wire of the LED signal. You can then just plug the LED signal back into the stock connector, clean and simple. I hate the idea of cutting off connectors on the bike side, you never know what you may want to do in the future.