they of course work best, when used in combination.
the player understands, that some things have been given a specific color for a specific purpose. traffic lights are red or green to tell us something, clothing is colored for a purpose, colors are used as labels and so on. the player also understands, that there are some things that just happen to have a certain color without a purpose behind it. a rock is grey, just because he is and the sky is blue because of the weather. the player learned from real life to give more attention to colors, when they have been put there by humans for the purpose 