It appears that the 2021 P51 FP is now available in the UK

[Sheptonian]

Just to add to what proteus has said, the new 51 in Plum is a long way from the Archbishop's new Advent chasubule shade shown on the Parker pen site. Instead in the flesh I was pleasantly surprised to find that it is very much an Aerometric Plum as you can see from the photo.

I agree that the Midnight Blue is a spot-on match with the Aero colour but curiously it is the Black CT version of the new 51 that reminds me the most of an Aerometric. Strange, given that dimensionally it is identical to all the others but there you have it. Probably because Classic Black Aeros are so common I suppose.

20210405_085558.jpg