[quote=@Frettzo]
[@Muttonhawk], yeah. I've been thinking of what to do once I've got time in order to earn some money and since I'm a graphic designer, I thought I could give it a shot.
[/quote]

Well, I don't know the first thing about the graphic design or colouring book industries, but I can at least confirm that adult colouring books are a thing. I do recommend you take a quick look at art therapy, though. Just to check it out.