These extra-thick coloring pages are so dazzling, you'll want to tear them out and frame them. The title says it all — this is an activity book, in all of its raunchy glory, is for adults.

Experts are questioning the therapeutic benefits of adult coloring books, one of 2015’s biggest and perhaps most-unexpected art trends, widely touted for its stress-relieving benefits.

From the queen’s quaint old pastime of collecting stamps to Prince Charles curious magic tricks to Kate’s more voguish adult colouring books – do you share hobbies with a member of the royal ...