I was looking for something else entirely and stumbled across a Mandala book which I took a closer look at because the cover is so pretty.
I did a search on Amazon and there are loads off books about this. Some of them position themselves as adult colour books and have mild claims of being soothing or meditative. I can see that it would be soothing if you are into that sort of thing, a bit like doing a jigsaw or watching raindrops on a pond. But some others have really weird and frankly unlikely claims like this one, or this.
How is it supposed to work? Surely it's just colouring in?
I apologise in advance to anyone who believes in this stuff being mystical or powerful because no matter how well you explain it I still won't believe in it, although I will be interested in what you have to say.