"suppose for all sets of n horses, every horse in the set has the same color." But that is clearly not true if I have a set of n horses, n-1 out of which are b

"suppose for all sets of n horses, every horse in the set has the same color." But that is clearly not true if I have a set of n horses, n-1 out of which are black and one is brown. So the premise is already wrong.