That's quite amazing. For me, you simply make several color soldermask layers but the problem that I see is that no PCB software I know of really has graphical tools for drawing ducks...
It's not hard to make simple graphical output this way but the reason you can't easily find someone to make this is that there are limited soldermask colors, no one keeps them around, and you need to flush the nozzle of the machine twice.
Besides, I think what you show here is something else entirely, probably a single-pass color printer that squeezes out paint instead of ink.
But you need to ask them, they will tell you. I'd bet you send them a line art or whatever and they know how to build it.
I don't know if it's the "future" of PCBs, let's face it, the vast majority of PCBs toil in obscurity. In washing machines and dishwashers and novelty fart machines, etc
If this color process is easy and cheap enough, I can certainly see it as a very popular thing for hobbyists, hackers, and high-value items like dev boards, etc.
For sure I'd make a Commodore or Tektronix related PCB with this!