It's funny you mention it. I'm not a designer in any professional sense, but I've found myself thinking about colors purely as a communication channel. Namely I

It's funny you mention it. I'm not a designer in any professional sense, but I've found myself thinking about colors purely as a communication channel. Namely I came to the conclusion that you can shove at most 4 bits of information into it, 1 bit of rgb and a birght/dark variant (color blindness notwithstanding). Designs which try to pack more info into this channel then they should are doomed to fail. The real answer after colors are exhausted is to move to shapes as a differentiator. There's a few primary shapes just like primary colors. () [] <> ×. Just like colors, they can be mixed. People will guess that a tear drop shape is in some way a combination of whatever the circle and whatever the trianlge/diamond represent. Eg you're allowed to make [) and <). But once you try to mix too many outlines together it all becomes grey in a sense. Trying to put a square, triangle, and arch each on a quarter of the outline just becomes an amorphous blob rather than an intuitive merger of established symbols. In a very real sense, basic shapes are a form of color from the perspective of design elements.