Johanna Basford is a genius and I am a little bit in love with her Lost Ocean postcard series.
Postcards work so well - there's no pressure to finish the entire colouring book, plus you don't battle with a stubborn spine of a well-bound book whilst trying to get to the fiddly middle bits (left-handers and chequebook stubs is not a match made in heaven either).
So, I've invested in some Nice Pens and a Magnifying Lamp to ensure that my new hobby doesn't wind up making me blind, and a friend who recently left HK is now getting semi-regular aquatic pictures from me.
Colouring for Grown Ups? I'm down with it.