It is a bit surprising but I'm seeing adult coloring books around these days. Hard to see the reason. Maybe people who never learned to draw want to make their own graphic novel.
The idea was extended at Grovefest. There are lots of wall paintings around the neighborhood. Someone put up the lines for a new one and filled in the spaces with color coded numbers. The public was invited to fill in the tones. Not very creative work but fun in its way and the result was pleasing.