I managed to get through to the guy at Akzo Nobel who looks after the RAN’s paint requirements.
Anti fouling is painted on in 3 coats. It is painted on Black, Plum or Pink and then the topcoat is Black. Plum becomes visible when the black wears off, the black paint does not change colour. Plum rapidly goes to a Light Grey and Pink goes to a Whitish Grey. Then, when Black starts to become visible again, it is time for a repaint. It is likely that the old way may be used again going forward.
The old black anti fouling i.e. DEs, FFGs when they first arrived was painted on black, black & black. No other colour was visible. Although it did look dirty brown after a while due to the muck in the water.
Also, the Storm Grey hull etc. paint these days is no longer Gloss, it is a low gloss with a relectance of 15%.