Finally, take a look at Rutledge’s third image to see what happens when we use the same shapes, but change the size and color.
With all the same shapes, the viewers here will mentally divide the items by color rather than size.
As Rutledge explains, that puts the hierarchy of similarities, from most to least potent, as color, then shape and size.
This hierarchy owes itself to evolutionary psychology. When scanning our surroundings, size and shape might be hard to determine due to all the visual intricacies, but colors immediately pop out to us. Just think about how you innately know that a bright red snake is not to be messed with.
But knowing about the different options is only half the battle. Knowing how to apply them is what matters.