Paint-By-X

Paint-by-X is a visual extraction element involving coloring or shading certain regions or spaces based on some sort of criteria. The 'X' in the element's name can change to any number of things, but they all come back to the same principal of painting by some factor.

This is not to be confused with paint by number kits, which while they may be an inspiration for the element's use, are usually unrelated to a given puzzle's functionality.

Puzzle Application
Paint-by-X puzzles work best with answers that can be expressed visually (or answers that are themselves pictures), or shorter answers that can be easily written via the shaded regions.

The X in the element name can be replaced by many things, depending on the subject of a given puzzle. Word puzzles benefit well from letter-based shading, while numbers are best applied to logic puzzles. Grids allow for the inclusion of coordinates, assuming a particular system is established during the puzzle. One particular variant is less common but still worth mentioning due to the ingenuity required to pull it off, and the fact that it has an established name. Geographical painting usually involves a particular region or country, with subdivisions being the target of coloring efforts. This type of puzzle is colloquially known as a Paint The Town puzzle, although not all instances of them involve actually painting towns.

Another clear divide in paint-by-x puzzles is the type of painting that is done. Color-based shading will usually require a specific instruction given in the puzzle, whether overtly or covertly. This is to ensure that the correct colors (or specific shades if necessary) are used, and that there is enough information to assign colors to particular spaces. There are certainly cases when instructions are not needed, such as when the core concept of a puzzle involves selecting items from a map or array that are already assigned a color (such as an election map), but unless there's a logical progression to that knowledge, it's best to include some indication.

Alternatively, a puzzle may simply rely on shading regions and ignore color entirely. In these cases, less instruction is necessary, and the puzzle may just draw attention to particular letters/numbers/locations, and have the solver realize that shading is necessary.

Played Straight

 * Space Filler (MITMH 2020) - While the method of assigning colors to cities in this puzzle is somewhat unorthodox (via phrases that normally have colors in them with the colors removed and a city added), the painting process is straightforward. All that they needed to do was color a map of Massachusetts correctly, and they get their final (picture) answer.

Notable Twists

 * Refreshment Stand (MITMH 2020) - Contained two notable twists on the element. First, the puzzle used crossword entries to indicate particular color:letter pairings, such as BLUE JAY (J --> Blue) and BLACK EYE (I --> Black). Secondly, the painting was not performed on the grid itself. Instead, solvers had to "paint" a physical object with identical dimensions by filling the holes associated with a given cell with a liquid that matched that cell's letter's color. Since the holes were interconnected, it meant that 'painting' one space often meant painting a much larger space than originally intended.