Cells are represented by some state (A, B, C, etc.).
On each tick, each cell takes the state of the largest non-majority of its neighbors. In the event of a tie, a cell keeps its current state.
Patches of two states stabilize towards clusters of maze-like patterns, while patches of three or more states exhibit chaotic behavior. (Although there are three possible states in the randomly-generated seeds, all states are represented as either light or dark to better illustrate the behavior around cluster borders.)
Shading is smoothed over an eight generation window. Original unsmoothed version here.