Blue is one of the colours we consider primary. We distinguish two of its shades in the rainbow (blue and indigo) and both shades also appear in the two main colour models, additive RGB (blue) and subtractive CMYK (cyan).
We have nicknamed our planet the “blue marble” and “a pale blue dot.” The color of the sky and sea, however, is more the exception than the rule among animals and plants.
Why? It is a combination of evolutionary and chemical reasons that begins in the plant kingdom.
But first, let’s remember some basic notions about color science. Colors are just our brain’s interpretation of a fragment of the electromagnetic spectrum, that of visible light. Each frequency in this segment is associated with a color, from the lowest frequencies that we interpret as red to the highest frequencies, blue.
The colour of objects therefore depends on the frequency or frequencies at which they emit or reflect light. With some bioluminescent exceptions, in the case of animals and plants it is a reflection of light. In these cases, if we see something blue it is because it absorbs the light that reaches it in other ranges of the spectrum and reflects the higher frequencies.
Among plants, the dominant colour is green, and one of the reasons is the optimisation of resources. Plants owe this colour to chlorophyll, which they use to carry out the process of photosynthesis. A blue plant would be less efficient in carrying out photosynthesis, since it would be returning the most energetic frequencies from the entire spectrum to keep the rest.
But the absence of blue goes beyond the plant’s leaves; it also affects the flowers, of which only about 10% have blue pigmentation. Researcher Kai Kupferschmidt explained the reason to Live Science. The molecules that absorb the red side of the spectrum and return the blue, he explains, are usually large in size, which makes them difficult for the plant to synthesize.
If, despite this, there are some plants that do dye their flowers blue, it may be because this rarity could give them a small evolutionary advantage: that of distinguishing themselves from other plants among pollinators.
And the animals?
Many animals live up to the “we are what we eat” maxim, at least when it comes to their skin color. Some of the pigments are due to diet.
This is the case, for example, with flamingos. These animals feed on algae rich in carotenoids, the precursor chemicals of vitamin A, and on crustaceans that also consume these algae. Carotenoids are the pigments that give colour to carrots and other vegetables and, due to their position in the food chain, to these birds.
Carotenoids can even color our own skin. This happens with excessive consumption of these chemicals: when our body cannot convert them into vitamin A, they are usually stored in different parts of our body,
But the blue color has no analogue to carotenoids, so there are no similar cases in the animal kingdom. This, again, does not mean that there are no blue animals, but the examples of animals that owe their blue color to pigments are very limited. Blue animals have another trick.
And that trick is nanostructures. This coloring method is based on iridescence. These nanostructures reflect light in such a way that most of the wavelengths end up being cancelled, while the blue wavelengths are able to “escape” to the outside.
An example of this are butterflies of the genus Morpho, whose wings have scales with this type of nanostructure. The phenomenon also occurs in the plumage of some birds such as the blue jay (Cyanocitta cristata), in mollusks such as the poisonous blue-ringed octopuses (genus Hapalochlaena) or fish like the royal surgeonfish (Paracanthurus hepatus), including mammals such as the golden snub-nosed langur (Rhinopithecus roxellana).
As in everything, there are also exceptions. In the case of the animal kingdom, rare reviews The blue color is another butterfly: those of the genus NessaeaButterflies in this group are the only known animals that produce blue pigments rather than relying on microscopic structures.
There are those who believe that the lack of blue animals and plants is a factor that has contributed to the linguistic development of colours. Humans did not begin by distinguishing all colours at once, but rather our societies gradually added new compartments to the palette. From the distinction between light and dark we probably went on to distinguish colours such as red, green or yellow.
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