What I mainly got out of this was that cheap eyeshadow palettes are a great alternative to professional powder-based resin dyes, cocoa powder can work great if you want to cast a brown or black thing, and food colouring or Kool-Aid will at least work with art resin (another resin caster in the comments says the moisture will definitely mess up polyurethane but epoxy can handle a little bit of it).
As a cosplayer who’s considered trying resin casting for props, I certainly sat up and took notice about the makeup one, since that’s an application where the more colours you have to work with the better. It seems they share their active ingredient, mica powder, with many of the powders actually intended for dyeing resin.