I did some more digging into the complexity of the biology and neuro-physiology behind the process of how we see and perceive color (and thus how we interpret not only the world around us, but how we might interpret and “allegorify” notions like the chakra color system). There is a phenomenal and enlightening chapter from David Hubel’s Eye, Brain, and Vision available for reading online and download, at the link. Following are some excerpts from Chapter 8, Color Vision, which I found to be pertinent for me in these contemplations of mine (For ease of understanding, I’ll post the Conclusion first, so you can see better where this complex information is headed; all emphases are my own; and be sure to see the final important statement at the end of this article….Everything we do depends on the brain!):
The subject of color vision illustrates so well the possibilities of understanding otherwise quite mysterious phenomena—the results of color mixing or the constancy of colors despite changes in the light source—by using a combination of psychophysical and neurophysiological methods. For all their complexity, the problems presented by color are probably simpler than those presented by form. Despite all the orientation-specific and end-stopped cells, we are still a long way from understanding our ability to recognize shapes, to distinguish shapes from their background, or to interpret three dimensions from the flat pictures presented to each of our eyes. To compare the modalities of color and form at all may itself be misleading: remember that differences in color at borders without any differences in luminous intensity, can lead to perception of shapes. Thus color, like black and white, is just one means by which shapes manifest themselves.
The result of mixing paints is mainly a matter of physics; mixing light beams is mainly biology.
In thinking about color, it is useful to keep separate in our minds these different components: physics and biology. The physics that we need to know is limited to a few facts about light waves. The biology consists of psychophysics, a discipline concerned with examining our capabilities as instruments for detecting information from the outside world, and physiology, which examines the detecting instrument, our visual system, by looking inside it to learn how it works.
….Light is defined as what we can see. Our eyes can detect electromagnetic energy at wavelengths between 400 and 700 nanometers. Most light reaching our eyes consists of a relatively even mixture of energy at different wavelengths and is loosely called white light. To assess the wavelength content of a beam of light we measure how much light energy it contains in each of a series of small intervals, for example, between 400 and 410 nanometers, between 410 and 420 nanometers, and so on, and then draw a graph of energy against wavelength. For light coming from the sun, the… shape of the curve is broad and smooth, with no very sudden ups or downs, just a gentle peak around 600 nanometers. Such a broad curve is typical for an incandescent source. The position of the peak depends on the source’s temperature: the graph for the sun has its peak around 600 nanometers; for a star hotter than our sun, it would have its peak displaced toward the shorter wavelengths—toward the blue end of the spectrum, or the left in the graph—indicating that a higher proportion of the light is of shorter wavelength…. If by some means we filter white light so as to remove everything but a narrow band of wavelengths, the resulting light is termed monochromatic.
The energy in a beam of light such as sunlight contains a broad distribution of wavelengths, from 400 or less to about 700 nanometers. The gentle peak is a function of the temperature of the source: the hotter the source the more the peak is displaced towards the blue, or short-wave-length, end. Monochromatic light is light whose energy is mostly at or near one wavelength. It can be produced with various kinds of filters, with a spectroscope containing a prism or a grating, or with a laser.
Most colored objects reflect light that is generally richer in some parts of the visible spectrum than in others. The distribution of wavelengths is much broader than that for monochromatic light, however.
…What color we see, I should quickly add, is not simply a matter of wavelengths; it depends on wavelength content and on the properties of our visual system. It involves both physics and biology.
…The pigments in the three cone types have their peak absorptions at about 430, 530, and 560 nanometers, as shown in the graph below; the cones are consequently loosely called “blue”, “green”, and “red”, “loosely” because (1) the names refer to peak sensitivities (which in turn are related to ability toabsorb light) rather than to the way the pigments would appear if we were to look at them; (2) monochromatic lights whose wavelengths are 430, 530, and 560 nanometers are not blue, green, and red but violet, blue-green, and yellow-green; and (3) if we were to stimulate cones ofjust one type, we would see not blue, green, or red but probably violet, green, and yellowish-red instead.
….The three cones show broad sensitivity curves with much overlap, especially the red and the green cones. Light at 600 nanometers will evoke the greatest response from red cones, those peaking at 560 nanometers, but will likely evoke some response, even if weaker, from the other two cone types.
Thus the red-sensitive cone does not respond only to long-wavelength, or red, light; it just responds better. The same holds for the other two cones.
…Color is the consequence of unequal stimulation of the three types of cones. Light with a broad spectral curve, as from the sun or a candle, will obviously stimulate all three kinds of cones, perhaps about equally, and the resulting sensation turns out to be lack of color, or “white”….
…To understand what is happening we need to know that the blue cellophane absorbs long-wavelength light, the yellows and reds, from the white and lets through the rest, which looks blue, and that the yellow filter absorbs mainly blue and lets through the rest, which looks yellow. The diagram on this page shows the spectral composition of the light each filter passes. Note that in both cases the light that gets through is far from monochromatic, the yellow light is not narrow-band spectral yellow but a mixture of spectral yellow and shorter wavelengths, greens, and longer wavelengths, oranges and reds. Similarly, the blue is spectral blue plus greens and violet. Why don’t we see more than just yellow or just blue? Yellow is the result of equal stimulation of the red and the green cones, with no stimulation of the blue cone; this stimulation can be accomplished with spectral yellow (monochromatic light at 580 nanometers) or with a broader smear of wavelengths, such as we typically get with pig- ments, as long as the breadth is not so great as to include short wavelengths and thereby stimulate the blue cone. Similarly, as far as our three cones are concerned, spectral blue light has about the same impact as blue plus green plus violet. Now, when we use the two filters, one in front of the other, what we get is what both filters let through, namely, just the greens. This is where the graphs shown on this page, for broad-band blue and yellow, overlap. The same thing happens with paints: yellow and blue paints together absorb everything in the light except greens, which are reflected. Note that if we used monochromatic yellow and blue filters in our experiment, putting one in front of the other would result in nothing getting through. The mixing works only because the colors produced by pigments have a broad spectral content.
… Presumably, some time in the distant past, a primordial visual pigment gave rise to rhodopsin, the blue pigment, and the common precursor of the red and green pigments. At a much more recent time the X-chromosome genes for the red and green pigments arose from this precursor by a process of duplication. Possibly this occurred after the time of separation of the African and South American continents, 30 to 40 million years ago, since old world primates all exhibit this duplication of cone pigment genes on the X-chromosome, whereas new world primates do not.
…We can think of Hering’s yellow-blue and red-green processes as separate channels in the nervous system, whose outputs can be represented as two meters, like old-fashioned voltmeters, with the indicator of one meter swinging to the left of zero to register yellow and to the right to register blue and the other meter doing the same for red versus green. The color of an object can then be described in terms of the two readings. Hering’s third antagonistic process (you can think of it as a third voltmeter) registered black versus white. He realized that black and gray are not produced simply by absence of light coming from an object or surface but arise when and only when the light from the object is less than the average of the light coming from the surrounding regions. White arises only when the surround is darker and when no hue is present. (I have already discussed this in Chapter 3, with examples such as the turned-off television set.) In Hering’s theory, the black-white process requires a spatial comparison, or subtraction of reflectances, whereas his yellow-blue and red-green processes represent something occurring in one particular place t in the visual field, without regard to the surrounds. (Hering was certainly aware that neighboring colors interact, but his color theory as enunciated in his latest work does not encompass those phenomena.) We have already seen that black versus white is indeed represented in the retina and brain by spatially opponent excitatory and inhibitory (on versus off) processes that are literally antagonistic.
….an object’s whiteness, blackness, or grayness depends on the light that the object reflects from some source, relative to the light reflected by the other objects in the scene…experiments showed convincingly that the sensation produced in one part of the visual field depends on the light coming from that place and on the light coming from everywhere else in the visual field….
Any color can thus be thought of as corresponding to a point in three-dimensional space whose coordinate axes are the three ratios, taken with red light, green light, and blue light…. to have color at all, we need to have variation in the wavelength content of light across the visual field. We require color borders for color, just as we require luminance borders for black and white. …differences across borders are necessary for color to be seen at all.
…If blob cells are involved in color constancy, they cannot be carrying out the computation exactly as Land first envisioned it, by making a separate comparison between a region and its surround for each of the cone wavebands. Instead ^ they would seem to be doing a Hering-like comparison: of red-greenness in one region with red-greenness in the surround, and the same for yellow-blueness and for intensity. But the two ways of handling color—r, g, and b on the one hand and b-w, r-g, and y-b on the other—are really equivalent. Color requires our specifying three variables; to any color there corresponds a triplet of numbers, and we can think of any color as occupying a point in three- dimensional space… …the blob cells making up the three classes are not like peas in pods but vary among themselves in the relative strengths of surrounds and centers, in their perfections in the balance between opponent colors, and in other characteristics, some still not understood. At the moment, we can only say that the physiology has a striking affinity with the psychophysics. You may ask why the brain should go to the trouble to plot color with these seemingly weird axes rather than with the more straightforward r, g, and b axes, the way the receptor layer of the retina does. Presumably, color vision was added in evolution to the colorless vision characteristic of lower mammals. For such animals, color space was one-dimensional, with all cone types (if the animal had more than one) pooled. When color vision evolved, two more axes were added to the one already present. It would make more sense to do that than to throw out the pooled system already present for black-white and then have to erect three new ones. When we adapt to the dark and are using only our rods, our vision becomes colorless and is again plotted along one axis, to which the rods evidently contribute. That would not be easy to do with r, g, and b axes… …Our tendency to think of color and form as separate aspects of perception thus has its counterpart in the physical segregation of blobs and nonblob regions in the primary visual cortex. Beyond the seriate cortex the segregation is perpetuated, in visual area 2 and even beyond that. We do not know where, or if, they combine.