Color Theory
The colors have meaning, and even if it isn’t explicit, it subconsciously informs the reader that this “thing” is connected to that other “thing.”

Learning color theory is, of course, a fundamental thing we all are either taught or stumble through as we figure ourselves out as artists. It’s also something that underpins how many humans interact with the world, just subconsciously. All that being said, I don’t think I really appreciated it until I encountered two texts that utilized visual cues in a very specific way to convey additional information.