It will work. It's a 10AWG cord, so good fro 30 amps. The wire colors are not perfect (should be red, black and green), but that does not do any harm.

@michael

thanks! And I assume this cord would work for the main power cord to the box as well? I am having an electrician put in a gfci breaker and outlet in my garage

This will not work for the main power cord. Remember, the main power needs 2 hot's, neutral and ground, so 4 wires.