It's done because I've got two other primed but unpainted tyranids ready to go and that feels like more fun than working on this one any more, which is good enough for the table. This is the way.
It's just drybrushing! If you look at the original model the detail on the armour is fantastic so it was really easy to drybrush some blue on. I did use quite a small drybrush to keep it accurate. I think on the actual GW nids those panels are flat so you need to actually draw the lines on to mimic this texture.
It's an Elegoo Mars 3 Pro with Siraya Tech Fast Abs-Like. On Lychee slicer there is a Vroom profile for this combo. Honestly I just set it to that, confirmed with a test print of the Cones of Calibration and it's printed almost perfectly since. Unbelievably good. It takes no skill at all :)