Abstract
I can't tell you how many times I have been asked "What does a graygreen look like?" or "Can you describe the color of the dark factor green?" I understand the question, but a clear and concise answer is not pos- sible without a common reference point.As an artist, I tend to think of color in terms of pigments - the actual paints I use everyday. However most people are not intimately familiar with the various pigments, and so I have had to be creative in choosing other examples in order to explain the various shades of green. Even those seem less than adequate to a person who is trying desperately to "connect" with my comparisons and envision the colors of the mutations.
For many years I wished for the opportunity to take comparison photographs of the various shades in all the mutations. Last August that wish came true. I had the pleasure of visiting Charles Collins in Baytown, Texas. I specifically set out to take comparison photos of nearly every color mutation of the Ring-necked Parakeets on his place and I came home with an exciting group of pictures.
The photo accompanying this column shows three green birds - three different shades of green. Using the wild type green Ring-necked Parakeet as our common reference (center bird), we can easily see the differences.
How is visual green produced? The visual color of green in most birds is not a simple, singular green pigment. Nor is it a mixture of yellow and blue pigments like you would find in a paint box. Instead, green is produced by a combination of the three elements listed below:
1. Melanins - black and/or brown pigment particles in the feathers
2. Carotenoids-yellow pigments in the feathers
3. Structural colors - microscopic bodies on the feathers that act like little prisms to scatter the light and reflect blue color back to our eyes.
The technical term for this scattering of light is Tyndall scattering. The microscopic structures on the feathers are called polygonal cells.
The microscopic prism-like bodies on the feathers - the polygonal cells, are colorless themselves, but require a dark background in order to reflect the blue. If the feathers have no other color in them except for the melanin pigments, then the bird will look blue. If however, the feathers have any yellow pigment in them, then the bird will look green.
How are the three different shades of green possible? Since all three birds are green, we know that they have both black (melanin) and yellow (carotenoid) pigments in the feathers. The variety of shades is due to a mutation gene that controls the shape of the microscopic prism-like bodies - the polygonal cells. If they are a squished or flattened in any direction to change the shape, the light passing through those cells will be a different color, or it may not reflect any at all.
In this case, since the polygonal cells reflect different shades of hlue light, we see a different shade of green on each of the three birds. If you were to take different shades of blue cellophane and hold them up to the light together with a yellow piece of cellophane, you would see different shades of green in much the same way.