You can conclude that H - {h1} and H - {h2} share the same color with each other because (assuming n >= 2), there will be a third horse h3 in both those sets. T

You can conclude that H - {h1} and H - {h2} share the same color with each other because (assuming n >= 2), there will be a third horse h3 in both those sets. Therefore by transitivity, these two sets must have the same color. This is implied and not explicitly stated, so it could be clarified.