Technically, there are several sets of possible "primary colors." A set of primary colors can be loosely defined as three colors, that when mixed, produce all the other colors in the rainbow. Cyan, Magenta, Yellow is a primary set, and so is RGB, which is the complment of CMY. Presumably one could define orange, green, violet (the compliments of RYB) as a "primary" set. There is no compelling physical reason to favor any of these options over another. The advantage to CMY or RGB is that they are exactly 120 degrees away from each other on the color wheel. But other sets of colors will work as "primaries" also. RYB works very nicely for kindergarten paints and food dyes. These paints and dyes ARE red and blue, NOT mis-named magenta or cyan. Kids and cooks easily make orange with RY, green with YB, and purple with RB.
I have no problems with teachers calling RYB "primary colors", since this is the common designation of primary colors in art classes. After they master RYB in kindergarten, kids will move on to experience other possible sets of primary colors - certainly CMYK computer printing inks, and RGB computer screens.
"Color" is half physics and half physiology. It depends both on the mix of wavelengths present AND the response of the human eye (and brain) to those wavelengths. Different people have somewhat different color perceptions. What I call "blue" or "blue-green," my mother consistently calls "green." As another example, one can perceive "yellow" with no actual wavelengths in the yellow part of the spectrum being present. Arbor Scientific sells a nifty set of theater gel samples with spectrum charts that show this phenomenon very well.
There some very nice color-mixer utilities associated with various paint, photo-processing, or word processing computer programs, all of which can be used for teaching color mixing. Even Microsoft Word has one. Some color-mixers give the options of working with an RGB system, a CMYK system, a color wheel system, or a hue-saturation-brightness (HSB) system. The students can then experiment with several methods of color mixing. In general, to find these, pull down the menu that lets you change the color of a font or "autoshape" in the drawing tool, then click on "more colors," and maybe "custom." One can easily build an entire lab activity around this. One might also consult with an art or graphics design teacher for more insights on what makes "color" and how the various color-mixing systems are used.
- Vickie Frohne
-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu]On
Behalf Of John Denker
Sent: Thursday, January 27, 2005 10:33 AM
To: PHYS-L@LISTS.NAU.EDU
Subject: Re: LED mini-flashlight price break
=============================
On the broader topic of playing with colored lights, it's
great fun to shine three primary lights (red, green, blue)
on the same place at slightly different angles, and then
interpose shadow puppets. You'll get at least three
different-colored shadows (cyan, magenta, yellow).
However be warned that a significant fraction of the
customers will not get it. They will insist on calling
the cyan area "blue", not just when it is alone but even
when it is in side-by-side contrast with a blue area.
They are not color-blind, since they can see that the
two areas are distinct; they are just vocabulary-impaired.
It's not just that they're untrained; many of them
have been explicitly mis-trained. There's about a 50/50
chance that when the kids were introduced to color theory,
they were told that the subtractive primaries were red,
yellow, and blue. That is, magenta was mis-called red and
cyan was mis-called blue. It makes my hair stand on end. http://www.google.com/search?q=paint+primary-color+yellow+k12
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