The dominant aesthetics at Zwarte Cross are full costume, rock, party and camp-practical. That is the visual language of the site, the stages, the merch, the crowd photos, and outfits that speak it look intentional rather than borrowed.
This is a costume festival, and that changes the maths: turning up in normal clothes is the conspicuous choice. Budget for one full look rather than three half-hearted ones, and make sure you can walk, dance and queue in it for eight hours.
What people actually wear: one good layer over a light base, because the temperature halves after sunset; wellies or waterproof boots on almost everyone by day two; the same jacket every day, because it lives in the tent and does everything; something identifiable, a colour, a hat, a flag, so your group can find you in a crowd of that size.