It won't make a difference which way it's hooked up other than possibly having the motor spin the wrong way, you can just do it random, and then swap any wires to reverse the rotation.
I can't find in the mamba manual where they say not to swap the white wire? I'm looking at it and they say it doesn't matter which way it's done.

Mine seems to arm when it detects the neutral position, as soon as I turn the transmitter on. If i've got the wrong transmitter profile selected it won't arm until I select the right one then it arms instantly.