https://en.wikipedia.org/wiki/CIE_1931_color_space

Original acrylic painting using red, yellow, and blue primary colors plus white

Color triangle with yellow, magenta, and cyan as primary colors

Original color study using a Josef Albers class assignment - Which is the "real" red, blue, and yellow?

Sardine can with primary red, ultra-marine blue, yellow, and black inks

My favorite class in graduate school was a psychology course on perception, taught by a kindly white-haired professor. It was just the right amount of content and complexity for me at the time, and a welcome change from trying to parse statistical formulas with my limited understanding of the notational world of algebra.

My favorite topic in this class was the perception of color, something that has always fascinated me. Two surprising things I learned: the color purple is not on the spectrum but rather is a construct of the way we combine blue and red in our minds. Violet and purple are often used interchangeably, but properly speaking, violet is more to the blue side and exists on the spectrum just to the left of dark blue or indigo, on most representations of the spectrum or "rainbow." There is a whole range of "non-spectral" colors! Who knew!

The second surprise was a graph of the "color wheel" for light that I am still struggling to comprehend. It looks like a triangle tilted to the left with a rounded apex. The apex is green; the other angles are blue and red. The vertical axis for this graph is the intensity of light and the horizontal axis is wavelength. This is the primary color wheel for light - not the color wheel you'd use for mixing paint pigments, for example.

I've concluded that there are any number of color wheels and color models, but some are more useful as a painter than others. Depending on which medium you use, you might want to switch back and forth.

In grade school, most of us learned that the primary colors are red, yellow, blue, and that red + yellow = orange, red + blue = purple, and yellow + blue - green. Try doing this with your Crayola crayons and you'll have a difficult time getting the colors to blend. For some reason, we give young children sloppy poster paints and what they create is .... sloppy posters. It's hard to work with water-based paint that has much more water than pigment and do a good job of color mixing or color harmony.

Later on in life, you might have learned to use two kinds of red, two kinds of blue, and two kinds of yellow, one "warm" and one "cool" to get more saturated secondary colors. Colors closer on the color wheel will produce mixtures that are more saturated and less muted. For example, to get a lively purple, blend magenta and ultra-marine blue, blending cadmium red and cyan will be more brownish or grey. Adding a touch of white brings out purple still more.

If you do a lot of ink-jet printing, you'll notice that the ink colors are magenta, cyan, yellow, and black. Sometimes the ink cartridges have labels like "light cyan" or "light magenta." This is because there is no white in this printing system.

When you are mixing light or working with pixels, it is almost like a mirror image world. Similarly, look at the primary colors in color photography. Here the primary colors are red (orangey), blue (purple-toned) and green. I remember when my Uncle Sy who worked for GE was telling us as children how color TV worked. I didn't understand most of what he said but was surprised that the colors were red, blue, and GREEN, rather than red, blue, and yellow.

I think this is all for now. I have some images of color models saved somewhere that I will include in the next installment.