For a long time I thought color was simple. I saw something and I knew its color. Why wouldn’t I? I had been taught my colors in kindergarten. This was reinforced in my feral childhood. A Northern Cardinal was clearly red. Sparrows were ‘little brown jobbies‘. Pine Warbler’s were bright yellow spots amongst the green pine needles. Egrets were white. You can tell snowy egrets because they have yellow feet. The Flamingos next to the Egrets were pink. Easy, peasy.
Blue Jays are blue. Well, yes and no. When I learned why this is so, I added ‘light scattering’ to my growing understanding that color is a very complex topic. Lot’s of physics – visible light is wavelengths of electromagnetic radiation in the range of 400–700 nm. Lot’s of neuroscience – the wavelengths captured by photoreceptors are distinguished by size and paired with specific stimuli, i.e., colors (colors are in effect synthesized). Why a specific stimuli is paired to a wavelength – a color we ‘see’ – is a mystery. There is thinking that it is evolutionary in nature. Our ancestors got a real survival boost when they could visually distinguish ripeness, or better yet, toxic plants. Nature often uses bright colors as warning signals.
So is this Blue Jay blue or not? We certainly see blue in a striking variety of shades. This is because the blue is a product of structural coloration, one of three sources of color in nature – pigmentation, structural, bioluminescence. In fact, Blue Jays have two of the three. The feathers grow as brown (or black as very, very dark brown) from melanin acting as a pigment.
The feathers also have nano-sized pockets – structures – made of air and keratin. When light strikes these structures, all of the wavelengths, except a select few, are absorbed and cancel each other out. The wavelengths not absorbed are reflected, captured by our photoreceptors, and sent to our brain for processing. These wavelengths just happen to be the size to be paired with the stimuli we perceive as ‘blue’. We ‘see’ a blue Blue Jay.
Eastern Bluebird 
Indigo Bunting
And it’s just not Blue Jays. It is all ‘blue’ birds. Blue pigmentation does not exist in birds. Pigments are in the foods the birds eat. Blue pigments such as those in blueberries are destroyed when digested by birds and don’t make their way into the feather structures. Blue is always structural and a feat of bioengineering that is precise and beautiful.
Aren’t we fortunate that the colors show up in photography the way they do in real life? Imagine if our eyes allow our brains to interpret the “colors” as colors but cameras only picked up black and white?
NONACHERYLK – thank you the comment. So interesting that you brought this up. How a camera system represents the light captured on its sensor in the colors we see on an output medium is a complex combination of science, engineering, and art. The camera’s processor (brain) is synthesizing the digital data sent from the sensor to represent the colors we will ‘see’. They are trying in many respects to master the mysteries of how we each perceive colors. In doing so, each manufacturer has their own take on Color Science. For many photographers, this color signature is an important subjective buying decision criteria. And, each photographer has the choice of manipulating the file colors, or not, in post processing to establish what they want to represent as their signature style. We are indeed fortunate that it is possible to show the colors in our photography that we want to represent in our image story. Thanks again for reading my post.