My Brain Hurts -or- A Discussion About Colors

Factual Questions
1

I’m in the middle of a fascinating book called “The Science of Superheroes” by Lois Gresh and Robert Weinberg. Essentially, they use the known laws of physics to see whether several comic book origions/powers are feasible. In the chapter concerning the Green Lantern (and about his weakness to the color yellow), they state:

All emphasis in the above quote is mine.

All of my life, I’d heard that the three primary colors were red, blue, and yellow. And that it was these three that produced all of the other colors through mixing. I have never heard of subjective primaries in my life.

So, huh? Am I a misinformed yutz from Indiana, or did the authors make a mistake? If I’m wrong, someone please explain it to me like I’m a four-year old.

[sub]closed quote tag - DrMatrix[/sub]

2

It sounds like they are talking about light, and you are talking about paint.

I know that all the colors in light mixed together make white(ish), and that when dealing with paint, it’s pretty much the opposite.

In the quote, it sounds like they start out talking about the colors present in sunlight, but end up talking about pigments.

3

Dammit…i forgot to close the quote. Could I please get a mod to fix it? Thanks!

4

Red, blue, and yellow are the shorthand primary colors for art students, but they’re not exactly correct.

First of all, when you think about color, you have to think about whether you’re talking about LIGHT, or PIGMENTS. (Yes, nitpickers, I know it’s all light in the end …)

From our art class days, we’ve been used to dealing with PIGMENTS–subtractive colors. What pigments do is absorb light, and reflect only a tiny portion of the spectrum. Thus, when you have a blank white page, with no pigments, it absorbs nothing, and reflects all of the visible spectrum. On the other end of things, when you mix together every color of paint you have, you lay down pigments that absorb all of the visible wavelengths of light and reflect none (effectively … naturally, some light still bounces back … it’s not a black hole).

Now, when you talk about LIGHT–additive colors–, everything’s backwards. The easiest way to think of this is when a stage hand at a play throws different color spotlights onto the dark stage, where they overlap, a mixed color is created. If you have no lights on at all, you have black. If you turn all the colors onto on espot, you’ll get white.

Handily, this (light/additive) method is what your computer display uses … which brings us to the primaries themselves.

The additive primaries are Red, Green, and Blue–hence the RGB monitor. By mixing together different amounts of red, green, and blue light, you can create all of the colors (or white, if you mix all equally).

ADDITIVE:
Red + Green = Yellow
Red + Blue = Magenta
Blue + Green = Cyan

When you talk about the Subtractive primaries, you go to those three products, Yellow, Magenta, and Cyan; this is why some computer image files and color printer inks bear the CMYK label (Cyan Magenta Yellow blacK; a darker black is added for printing purposes, since the mix of the other three is never perfect, end usu. ends up as a muddy brown rather than a proper black).
In brief, Red Yellow Blue is a good enough shorthand for most art students, but it’s really just approximating the true effects of Magenta Yellow Cyan, the proper subtractive/pigment primaries.

Why do we do that? Because Magenta and Cyan aren’t in our day-to-day vocabulary. Red and blue are close enough.

5

There’s an anecdote in Richard Feynmann’s book “Surely You’re Joking, Mr. Feynmann!” about the exact same thing (primary colors for light vs. primary colors for paint). It’s a pretty funny story, and Feynmann is a cool guy anyway. You might want to look it up.

6

What Toadspittle forgot to mention was that subtractive primaries mix together to form the additive primary colours.

SUBTRACTIVE:
Yellow+Cyan = Green
Cyan+Magenta = Blue
Magenta+Yellow = Red

And as he said because of imperfections in the ink, black must be added to form true black.

7

Sigh. They were wrong, and so were you. Sort of. I don’t think a child can understand it, so you have to fasten your seat belt.

There is no such thing as a primary color in nature. Nature has a spectrum of wavelengths. Light that is visible starts at red (long-wavelength photons) up to violet (low-wavelength photons). In nature, green is not a mixture of blue and yellow – there is a just a narrow range of photon wavelengths that are green. However, what looks green to the eye and brain is a different story.

The human eye responds to peculiar combinations of certain wavelengths, and the brain perceives the combinations as a spectrum of colors. Green photons look green, but so does a mixture of blue and yellow photons.

Red/Green/Blue is not a physical absolute, it’s a convention created by the International Commission on Lighting, which established wavelengths that correspond to primary colors: 700 nm for red, 546 nm for green, and 436 nm for blue. RGB works well in computer screens to create your perception of all colors.

But, you can also create all perceived colors by mixing tints of red/blue/yellow. Both RGB and RBY and (CMYK for that matter) can be mixed to create the perception of all colors.

To understand this, and why the authors of the book were wrong, you have to understand how color receptors in the retina work. And how the brain mixes them to create a perception of color.

“The retina contains three types of cones. Different light sensitive pigments within each of these three types responds to different wavelengths of light. Red cones are most stimulated by light in the red-yellow spectrum. Green cones are most stimulated by light in the yellow-green spectrum. Blue cones are most stimulated by light in the blue-violet spectrum. This phenomena describes the spectral sensitivity of the eye.”

The authors of the book have mistaken the perception of color with the physics of color. For example, there is no photon with the color white. There is no such thing as white light. White is a perception that the brain creates when all red-yellow/ yellow-green/ blue-violet receptors in the retina are stimulated – white exists only in the mind. Perception of light color is different from light physics.

Sorry, I know this is complicated, but you were right that they were wrong.

For a typically wrong idea about color, see this site.
http://www.firelily.com/opinions/color.html

For an accurate description of color see this site
http://www.luminous-landscape.com/tutorials/color_and_vision.shtml

8

Sorry, BOTH links above give a good description of color, thought the second one has more understandable graphics. It’s easier to read.

Originally I had included a link to a bad description of color, but changed my mind at the last minute.

9

Cecil Adams on If blue, red, and yellow are primary colors, why do color TVs use blue, red, and green?