First, make no mistake: Colors are not “out there.” Our retinas and brains create the colors as responses to invisible magnetic and electrical stimulations. The whole visual scene happens within our skull as a correlative event, where we and the so-called outside world act together. Nature and our minds are one entity.
The stimulations that produce our sensations of red or green vary in how closely the waves of electromagnetism (EM waves) are spaced. This allows colors to reveal secrets of the universe.
I have no idea how autumn colors get created in leaves, so I’ll get right to this topic in pretty much a general way. There are two categories of colors: Category I consists of the EM waves or colors emitted by the Sun and all the stars, bodies like the Moon and planets that reflect sunlight and fire and lightbulbs. These are the spectral colors. You know them well, because they’re the ones in a rainbow: violet, blue, green, yellow, orange and red. They include the three primary colors of light: red, green and blue – and combinations of these three can produce every other possible color, thanks to the architecture of the eye.
Category 2 includes all other colors, which Nature produces by either mixing spectral colors or else having waves interfere with other waves, a process called diffraction. These are seen on cloud edges, peacock feathers, mother-of-pearl seashells or oil slicks. They contain all sorts of cool things like maroon, pink, aqua, teal and exquisite hues that I can’t even name. No star emits any of these, and they’re not found in fire or sunlight.
Of the basic spectral colors, red is Nature’s favorite. It’s the hue emitted by hydrogen when it’s stimulated. Since hydrogen is so common, so is deep red. It repeats like a musical coda throughout every cosmic village and paints every glowing nebula everywhere.
Orange is the dominant color of the coolest, most common stars.
Yellow is what the human eye experiences when it receives an equal blast of red and green. There really may not be such a thing as true yellow in the universe. In any case, a pure saturated yellow is very close to nonexistent beyond Earth. Some books state that our Sun is a yellow star, but of course this is not true. Our Sun is pure white, as astronauts have always reported. It looks pale lemony from the surface here because a bunch of its incoming blue has been subtracted and scattered out to give us our blue sky, leaving the remaining sunlight with a slight green and red excess, which once again combine to appear yellow.
Green is a fascinating color. It is the Sun’s strongest emission, and hence the one to which our eyes are most sensitive. We see green more readily than any other. Yet there are no green stars and only one green planet (Uranus). It is the glow emitted by glowing oxygen, so it is usually the only color visually seen in an aurora.
Blue is the color that most adults like best, according to surveys. Across the universe, it means “hot.” Only the hottest stars are blue-white, like Vega overhead these nights at nightfall.
Violet is an exquisite color, in my opinion, but rarely seen thanks to our eyes’ insensitivity to it. The daytime sky is actually violet, which many birds and insects perceive. But we humans instead see the sky as blue, since that color is also plentiful in the sky and our retinas pick it up far more readily.
There’s far more to the story, of course; but I hope that everyone can enjoy this sort of brief primer on the basics of color, now that our terrestrial world is erupting with them.