Colourfields

Over on the (inexplicably login-walled) site "NewEnigma," Keith Austin [writes](https://www.newenigma.com/enigma/view/1277/Colourfields): > Draw a 4-by-4 grid. Colour each square red or blue. Select any square, S, and write 1 in it. > Then write 1 in every square you can reach from S by a series of moves, where each move is from > a square to an adjacent, horizontally, vertically, or diagonally,…