A puzzle that requires adding colour to an image to reveal a hidden message.
A colouring puzzle requires the player to colour in parts of a outlined image.
Colouring is combined with another mechanic to produce a puzzle. Basic math is commonly used, where the answer to equations determine the colour of a region. Icons within the region can also used to create patterns, as well as further combined with logical constraints.
The blank image can either be a silhouette or a tile pattern.
A silhouette is an outlined image, where objects are visible even with out the colour. In order for there to be a hidden message the divisions of the objects must be ambiguous — colouring will be required to determine what is the relevant information.
A tiled pattern is one or more shapes repeated across the entire colouring page. The individual shapes will need to be marked in some way, or identifiable, in order to colour them correctly.
Most colouring puzzles have only a single colouring pattern that produces the desired result.
A layered puzzle uses the same stencil with an alternate colouring pattern to produce a different result.
Assume everything in this reference is a working draft, there's prone to be some mistakes and inconsistencies. I figure it's best to publish and get feedback rather than write for years in secret. The terms will change, the structure will shift, and the bugs will be chased out. It'll take a while.