I was just thinking about how most humans see in three basic colors which are red, green, and blue so we see in three dimensions of color because we are trichromats and we see all other colors by combining red, green, and blue in different ratios and amounts. This means we see three dimensions of color and the best way to represent the colors we see would be through a color cube. Each color that we see has a coordinate along the red, green, and blue axis. White would be the maximum coordinate along the red green and blue axis while black would be the minimum along all the axes.
Dichromate see two dimensions of color which are red and blue so a person who is red green color blind sees two dimensions of color because all the colors a dichromate sees can only be produced by combining green, and blue. The colors that a dichromate sees would be best represented by a square with each color on a green, blue as a blue, green corordimant.
Monochromates can only see in one dimension of color as they can only see how bright something is but not what wavelength of light something is. The way monochrates see would be on a line with only shades between black and white.
Some species such as some birds and reptiles can see up to four basic colors red, green, blue, and some ultra violet. Tetrachromates can see up to four dimensions of color as they can see any color that can be produced by combining red, green, blue, and ultra violet so the way they see color would be best represented by a teserect with each color on a red, green, blue, ultra violet coordinate.
So by adding just one additive primary color it is possible to increase the number of colors exponentially because the new number of colors is the number of old colors times the number of brightness’s of the new additive primary colors. So if we could see a fourth primary color we could see many more secondary colors.