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Tuesday, August 21

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Color: in the eye of the beholder?

Try to imagine a new color. Well, just stop, because it is not possible. Every color that you can imagine is simply a mixture of the red-green-blue wavelengths that comprise the Human Visual Spectrum. There are plenty of other wavelengths wandering through the universe, but our eyes cannot detect them. We live our life in the red-green-blue world. If you are old enough to remember the first big-screen projection-style TVs, you’ll remember that there were three lenses projecting onto your big screen—a red one, a green one, and a blue one. So, all your favorite movies were projected (only) in the colors that you can see. As you compare different vertebrates, you realize that they have different visual receptors that will detect various subsets of the human-normal red-green-blue spectrum. For example, many carnivores are often characterized as color-blind, or only seeing in black and white. This is an over-simplification, but it gets across the point that not all animals can detect the same wavelengths.

There are other wavelengths out there, however, that no animal can detect, for example, X-rays or radio waves. There are wavelengths that some animals can detect, but others cannot. Infrared wavelengths (associated with heat) can be detected by many snakes, but I’ll save that fun topic for another blog post someday. Ultraviolet light has complex interactions with the biological world. Humans cannot detect it visually, yet it causes sunburns and skin cancer in some. Yet we also need it to support the myriad purposes that Vitamin D provides to our bodies. Many lizards require it for a functional metabolism, yet some do not. Birds and (at least many) insects can detect it.

These last examples lead me to my point for this blog. Color, very literally, is in the eye of the beholder. Color also is relevant only in the context of its situation of illumination. In my classes, I often use the examples of our familiar red snapper and American crow. I anticipate that everyone knows that the fish is nearly uniform pale-red in color, while the crow is pure black. The problem is that these statements are not purely true. Red snappers are red when we see them, at the surface of the water if we are fishing, or on ice at the market. Red wavelengths do not penetrate water to the depth where these fish live. Thus, it is impossible for them to appear red in color where they live. They are gray/black and virtually invisible at those depths. Why they appear red in color at the surface of the water and on ice is explicable in terms of wavelength physics, but less so in terms of the natural history of the fish. So, take it on faith that red snappers simply are not red in their daily normal lives. A nice summary of this phenomenon appears in the link referenced below.

Birds really test the limits of our ability to “see” into their visual world. Any visitor to Zoo Atlanta will understand that the diversity of birds display an amazing variety of colors. But, none of us get the point. Birds can detect ultraviolet wavelengths, and this means that we absolutely cannot see the coloration of a bird in the way that another bird can see it. If you think a crow is black, the fact is that you simply do not know that (from a bird’s perspective). Bali mynahs are mostly white? Maybe not if you’re a bird. If you do a web search for “ultraviolet coloration of birds,” you will find computer-corrected images of familiar birds, showing unfamiliar colors. While these digitized images help reinforce my point, they also badly miss the point. Humans cannot see what we cannot see. We can only see in digitized images the wavelengths that we can see. Birds, insects, flowers, and who knows what else surely reflect colors that are beyond our perception and, by definition, beyond our imagination.

At a recent conference, I attended a fascinating presentation by Dr. Suzanne Amador Kane, of Haverford College, during which she completely up-ended my entire perspective of the amazing coloration and patterns on the tails of the male Indian peahen (Pavo cristatus), or what we usually refer to as a peacock. Her work on that topic has yet to be published. But, let’s just say that looks can be deceiving— blue is not always the blue, nor perhaps the new black.

A nice review of the realities of coloration in the ocean depths:

Joe Mendelson, PhD
Director of Research

Connect With Your Wild Side #onlyzooatl