I wish I'd designed my own range of Adult colouring books now!!
As long as 20 years ago I was using adult colouring books for groups of older people To whom I taught Art and craft. Quite often I would draw out a very simple picture and photocopy it for a few to use.
For some people who had had strokes for example it was a great way to get them involved in something enjoyable. Others were daunted by a white sheet of paper and weren't confident to have a go at painting. Some didn't even have the confidence to sit with a group of "artists" so these were a great way to at least get them up to the table and joining in. After a few weeks colouring in I'd be able to get them to try painting and for quite a few their spare time was transformed and they would come in telling me that their family had bought them paper, paints, art books etc. and we're really encouraging their new hobby. It was rewarding for all of us.