- Each pixel represents a cell
- Each cell has one of 16 colors (numbered 1 to 16), which are assigned randomly at the start.
- The left and right edge and the top and bottom edge of the "playing field" are connected.
- At each turn, every cell that has at least one neighbour cell with a color that is one higher changes its color to that "next higher" color. Additionally color 1 is considered "next higher" to color 16.
As you can see, the random coloring of the cells quickly turns into little same-color pools, but then spiral-like structures emerge that soon fill the entire playing field, even though the rules do not mention any spiral-like structures.
And now for something awesome: you can get pretty much exactly the same behaviour with a chemical reaction!