I actually don't know, it's a good point. It's definitely stochastic, but I don't know how late in the development it happens. There are definitely cats with colours completely jumbled cats with large patches of each colour. But I just realised that colour comes from melanocytes. And melanocytes must migrate from the back, as they come from neural crest. Which strikes me as a great reason for straight division on the front (the cells coming from left and right meet there) that we see here, regardless of the origin of diversity of cell colours. So I think it shouldn't matter, but it's just a guess.