When someone asks you what color snow is, you say white, not none. Black, white, and gray are not hues, but I think it is hard to say they are not colors.
A more thorough treatment should mention color spaces and standards, additive and subtractive mixing, digitization, optical effects, vision and perception in other animals, etc. The one standard reference on the non-biological science that everyone cites is The Reproduction of Colour by Dr. R. W. G. Hunt. Perhaps someone else can recommend a reference for the biological end of things? --LDC
I think it should go on the table since it is definitely a pure spectral color. The more we list, the better; I don't see how it helps to omit some pure spectral colors. The Encyclopedia Britannica lists it, but omits indigo. --AxelBoldt
red | 650 nm |
orange | 600 nm |
yellow | 580 nm |
green | 550 nm |
cyan | 500 nm |
blue | 450 nm |
indigo | 420 nm |
violet? | 400 nm |
You can't steal what someone gives freely. :-) --KQ
red | ~650 nm |
orange | ~600 nm |
yellow | ~580 nm |
yellow-green? | ~550 nm |
green | ~500 nm |
blue-green? | ~480 nm |
cyan | ~450 nm |
blue | ~420 nm |
blue/indigo | ~400 nm |
violet? | (mixture) |
violet?/magenta? | (mixture) |
--LDC
Violent and Magenta aren't really quite the same thing - it's a minor difference (like between indigo and blue), but magenta is not a spectral color.
I agree; this article is "color" not "electromagnetic spectrum". To me, that means it should focus on the human subjective experience of color. That's why I include all 360 degrees of the color wheel, and explicitly mention that the purples are mixtures rather than pure spectral colors. --LDC
Oh, and in the top table Indigo does not show up in Opera 5.0. I guess they don't recognize that tag, which IIRC should mean it's not technically W3C compliant. --KQ
I'd prefer the (correct) wavelengths to be there. After all, how else can you define "blue" if not by giving its wavelength? --Axel
You misunderstand my point--the wavelengths are correct, for some monitor with certain settings on some video card on some coomputer with some software. It is not possible for it to be correct on all of them, because HTML doesn't specify colors as wavelengths--as well it shouldn't, because that's not how human eyes perceive it anyway. --LDC
I'm not so concerned about the HTML colors -- of course they will be off on most machines. But I want the right color names for the right wavelengths. So if we call it cyan, it should be listed with cyan's wavelength and some vaguely cyan-like HTML RGB mixture. Also, the table occurs in the physics section of the article, and spectral colors are cleanly defined physically by their wavelengths. --Axel
Color perception isn't a binary operation where if a cone detects a color it sends a positive signal to the brain. In fact, image processing starts right in the eye itself. Rods and cones are divided in to roughly circular receptive fields. Each field represents input to bipolar cell, the type of neuron that carries visual signals back to the brain. I don't know whether or not the fields can overlap. In the center of each field is a circle whose diameter is about half the diameter of the field. The cells in the center of the field are either a type of cone or a rod. The outer ring of the field consists of rods if the inner field has rods, or cones that may not be of the same type if the inner fields have cones (in fact, I believe that the cones must be of a different type, since rods detect brightness). The inner field of cells inputs directly to the bipolar cell, and stimulating only that field increases the number of action potentials to the brain (n.b. there is a base line action potential frequency in the absence of light). The outer field inputs to a cell called the horizontal cell. The horizontal cell takes that stimulus and sends an inhibitory signal to the bipolar cell. This means that if only the outer field is stimulated the input to the brain can go down below baseline. If the entire field is stimulated, the exitatory signal will be greater than the inhibitory one because the number of cells giving the bipolar cell exitatory input outnumber the single cell giving the bipolar cell inhibitory input. Their numbers even outweigh the fact that the horizontal cell inputs closer to the axon hillock (still above the cell body, though).
Ok, so we have a physical description of the "pixel" of the eye, we're almost done explaining color. The trick is to realize that the surround will actually subtract its sensitivity from the sensitivity of the center to create the sensitivity profile of the field. So, when "Green" cones surround "Red" cones, subtraction of their sensitivity curves (with possible weight factors inherent in the physical design of the eye) yields a field with a peak sensitivity at 650 nm. Just by changing the arrangement of the cones ("green" center, "red" surround) yields a field with a peak sensitivity to about 500nm, a genuinely green field. Using this model, it is easy to demonstrate that the eye is sensitive to 6 different colors (9 if it is possible to have the same types of cones in center and surround).
Also note that this shows that some optical illusions are possible because of a design flaw in the eye itself: this field arrangement exaggerates high contrast boundaries in the signal to the brain. --BlackGriffen