Mosaic
Colour the grid so every number counts its black neighbours
Click a square to cycle it black, white, then empty; right-click, or Ctrl-click, cycles the other way. Drag along a row or column to paint the empty squares in its path; squares already black or white keep their colour. On a touch screen a tap cycles forward, a long press cycles back, and a swipe scrolls the board. Arrow keys move; Enter cycles forward and Space back. Ctrl or ⌘ Z undoes; Shift Z redoes.
Progress saves on this device. Boards too large for the screen scroll inside their frame.
How to play
Each number counts the black squares among the nine around it, including its own. Colour every square black or white so that all the numbers are right.
A clue turns red with a dashed outline when its neighbours can no longer give that count, and turns grey inside a ring once it is met with every neighbour decided. Clues left counts the numbers still to meet; the puzzle is solved when none are left.
Undo and Redo follow your history; a new move after Undo replaces the undone moves. Restart clears the board and can be undone. Solve reveals the answer; a puzzle finished with Solve does not count as solved.
Engine: Simon Tatham’s Mosaic, from the Portable Puzzle Collection. MIT license and credits.