I know it’s quite an old posting of cecils, but (there’s always is isn’t there) has anyone pointed out that there’s actually three visible colours (Red, Blue, Green) and all other colours are derived from these? And correct White is not a colour, nor is Black.
See http://www.straightdope.com/classics/a2_168b.html
Sorry, but you aren’t even close. Read a little about the physics of color. White is the reflection of all color wave lengths. Black absorbs the whole spectrum.
BTW, the three Primary colors, which I believe, is what you’re referring to, are Red, Blue and Yellow, not Green. Green is a secondary color, combining yellow and blue.
All colors in our visual spectrum are indeed, derived from the three primaries.The secondary colors are green (blue/yellow) purple (blue/red) and orange (red/yellow)
The color wheel may answer any other questions you might have.
Nitpick:
You’re both right. There are two sets of primary colors. Since it’s 5 am and I haven’t had my caffeine yet I can’t remember the technical terms, but there is the set yellow-blue-red which are primary for pigments, and the red-green-blue set that is primary for light. A yellow pigment and a blue pigment give you a green pigment. A red light and a green light give you a yellow light.
Cecil has weighed in on this topic, too:
If blue, red, and yellow are primary colors, why do color TVs use blue, red, and green?
Arjuna34
The strange thing about that column is the odd idea that the Greeks couldn’t see colors at all. Wonder what those “scholars” thought made the frescoes and mosaics appear so lifelike?
Primary and secondary colors have nothing to do with physics, but rather with physiology. To creatures with different eyes than our own, red, green, and blue (or red, yellow, blue, or whatever) would not necessarily be the primary colors, and they might not even have the same number of primary colors we have. The might even see in a continuum of color, in which case every color would be “primary”.
Red light and green light do not together make yellow light, they make a light which is indistinguishable, to our eyes, from yellow light. If I had a red laser, a green laser, and a yellow laser, and I mixed the red and green together, a human would not be able to distinguish that from the yellow laser, but some other organism might, and a spectrometer certainly could (indeed, to the spectrometer, they would look completely different, with no similarity at all).
I think some people are getting slightly confused between paint and light here.
Lifelike in color? Offhand, I don’t recall there being any surviving polychrome Greek art whatsoever.
There are historic color mysteries. Why does Homer repeatedly refer to “the wine-dark Sea”? Why do ancient astronomers call Sirius “red”?
Is this really possible? It doesn’t violate any physical principles, but the engineering may not be feasible. Off the top of my head, I can’t think of any detection mechanism that would work. I believe every detector will preferentially detect some wavelengths better than others.
So to detect light in a continuous manner, you’d need something analogous to the inner ear: an array of detectors, each tuned to a slightly different wavelength. This works well in the ear, because the each detector can sense or not the sound without attenuating signal. Is it possible to build something like this for light?
I’m inclined to think an imaging true-spectrum system might not be possible, but a true-spectrum and source-direction system might be.
It’s not hard to make a spectrograph out of organic materials. All you need is a focusing lens, a slit, a prism and an imaging detector (e.g. retina). But it will only make a spectrum along a slit. To get an image out of it, you need move this “eye” and scan across whatever you’re trying to see.