Travelling in the Colorspace

Color is fascinating to me. A prism divides light by frequency into a spectrum... so why is a color wheel a circle? (There is an answer and, by the way, purple which connects the two ends of the spectrum doesn't appear in the light divided by a prism). We think of a color wheel having primary colors like Red, Green and Blue. You can combine them to form the other colors. But, you could pick any three colors that are 120 degrees apart in the color wheel and use those as the primary colors and form all the others. Red and green are special to us because we have cells in our eyes to detect them. We also have yellow and blue detecting cells, as well as lightness detecting cells (for black/white distinction). Our eyes perceive some colors well and others poorly. Consequently the color wheel isn't really an even distribution of colors if you consider humans to be the observers. We can sense more differences in greens than we can in yellows - we have more green detecting cells in our eyes.

The color space isn't a sphere if you care how we perceive colors. It's not a regular shape at all. It's a weird, flattened spheroid with edges that are sometimes at large radii and sometimes shorter, depending on the hue.

Of course pigment colors behave differently than light colors, but we don't see paint by putting it into our eyes. We see the light reflected off the paint, so how colored light behaves still matters a lot to us whether we're working with pigments or lights.
The wikipedia page on color space models has so much more information than I ever imagined. There are some color models that treat color as if it were a uniform distribution, and some that treat color the way we perceive it. They are really different! We simply can't perceive as many different colors in some portions of the color wheel.

I've discovered some things that others have already invented about color. Nothing original, but it is new to me. If you draw a line between any two colors in a color wheel (even to different saturations of the colors) then you can use that line to determine what color will be produced by mixing various proportions of the two colors. Mix them 10:1 and you'll find the color at the point on that line about 1/11th of the way from one color toward the other. Mix them 50/50 and the color will be found at the midpoint of the line. If you pick so-called "complementary colors" (on opposite sides of the color wheel) and mix them 50/50 you get the color in the middle (brown or gray, depending on whether you are mixing pigments or light).

If color is a space, I imagine I am a traveller in it. I start at one color and add another to move to a different place in the space. My goal is to feel free within the color space to find a path to wherever I want to go, using whatever paint colors I might have. But, every step in this space has a cost if you value color saturation, because saturation is lost every time colors are mixed (in pigment colors at least, and probably with light too but I'm less sure of that).

I use this information to understand the rules of what people expect about colors - mainly, so I can break those rules. Only by questioning and breaking those rules can I find my way out of the mundane and dogmatic thinking about color I've grown up with. Give me purple and yellow. Give me Orange and Cyan. Give me colors that fight and argue and I'll make a painting that catches the eye and engages the heart.