They'll virtualize the ink jet printer ink model: Totally Transparent Liquid Glass UI is free, DRM'ed dye is an in-app purchase that fades over time, or subscription that you don't actually own.

User defined colors not possible, only expensive premium licensed Pantone, Disney Princess Pink, Barbie Pink, Tiffany Blue, Coca Cola Red, Cadbury Purple, UPS Brown, Target Red, Home Depot Orange, John Deere Green & Yellow, Vantablack, Stuart Semple Black 2.0, 3.0, etc.