#7 is a glaze so you want something soft for that since it doesn't really need any cut whatsoever. You could use the black/grey or blue pad.
Cleaner waxes, I would use something like a white pad, maybe even green or possibly orange, depending on the situation and the steps I want to take.
From my understanding, the red pad is one of the newer pads they offer and it's meant for applying waxes.