Is the Primordial Soup Done Yet?
More technically: each cell counts how many cells in its neighborhood, including itself, are of color 1; call this k. Then in the next click it becomes color 1 with some probability p(k), with p(0) = 0 and p(k) = 1 - p(5-k). I only used the case where p(1) = p(2) = 0.5.