Your blueberries aren't really blue.
In fact, most things in nature aren't actually blue.
The following is a minor study, and for many it may not be seen as much of a big deal. However, the findings are still rather interesting as it takes something that we don’t really think about and re-contextualizes it. I mean, has anyone ever really questioned why blueberries are blue? Honestly, I’ll admit that part of covering this study may be a minor interest due to picking up blueberries today. Either way, consider this some legitimate food for thought.
And if you happen to have blueberries or some bloom fruit at home, why not try removing some of the wax (maybe not with chloroform) and take a gander at the flesh underneath? Compare that color to the color with the wax and see for yourself if there is a noticeable difference.
Sorry for those who have felt betrayed by “red” onions, but recent research suggests that we probably can’t trust the “blue” in blueberries also.
In fact, we probably can’t trust most blue things in nature to be truly blue as the color blue itself is one of the rarest colors found.
That’s right- many things in nature don’t actually produce blue pigments, and instead what tends to appear blue seems to come from a bit of manipulation on the part of an organism.
The exact reason for why blue is rare isn’t quite clear, although it’s been alleged that blue color is far-too costly of an investment for organisms. Another argument may suggest that the source of some near-blue pigments in plants such as anthocyanins may be labile to pH and other factors, making them less stable if a consistent blue color is warranted. So instead of directly creating blue pigments, it appears that organisms have found other ways to appear blue.
One way is through a method called structural coloration, in which nanostructures help to interfere with direct pigment-visible light interactions in order to create the perception of blue.
In general, most things in nature contain pigments which reflect specific wavelengths of light. It’s the wavelengths that are reflected that we perceive through sight- a red apple reflects red light, leaves reflect green light, and so on.
In contrast, some organisms may utilize a unique organization of proteins or other structures which help to alter the wavelengths of light that get reflected, usually resulting in blue or other colors being perceived.
For instance, in some bird species such as Blue Jays a layer of keratin arranged with air pockets help to scatter visible light, resulting in blue light being reflected while the other colors become absorbed by an underlying layer of melanin.
Another example are peacocks, in which historical evidence has noted that the color of peacock feathers are actually brown, with accumulating research noting that differences within the lattice crystal structure of the barbules of peacock feathers are what contribute to the iridescent blues and greens that are so well-known.1
For morpho butterflies, the organization of two layers of wing scales are also what help to provide them with the stunning array of blues2:
So what exactly is happening with not-actually-blueberries?
Again, many dark-colored plants derive their color from anthocyanins. Blueberries themselves are full of anthocyanins, but anthocyanins are generally dark red/purplish in color, and not exactly “blue”. And in fact, when eating a blueberry you probably have noticed that they tend to appear reddish on the inside, raising more questions towards the source of blue.
However, recent research suggests that blueberries owe their blue color to structural coloration by way of a waxy coating.
The work conducted by Middleton, et al.3 suggests that the epicuticular waxes referred to as “bloom” on the surface of various fruits may help in refracting light and producing the blue color we see.
Epicuticular waxes appear to serve several purposes for the berry, including helping to control gas exchange and providing some physical barrier from microbes.
In the case of blueberries they appear to create both the blue color as well as the rough-looking, sometimes whitish surface of blueberries. You all have likely noticed it, and may have actually tried to remove them to no avail. The same may go for grapes as well!
Much of the research conducted in this study is above my head and focuses on a good deal of physics so I will not consider it for this review. Nonetheless, when researchers treated the surface of blueberries and removed the epicuticular wax they noted the loss of blue color. Not only did this occur with blueberries, but also with other bloom fruits as well including plums where the loss of blue is far more noticeable.
Altogether, the research points to a possible mechanism in which blueberries appear blue rather than producing blue pigments itself, adding to the majority of non-true blue organisms that exist in nature.
But why spend all this energy in appearing blue?
The authors suggest that the darker color of berries may cause them to appear more inconspicuous, and it may be through structural coloration via bloom that may make these berries more noticed by birds and other animals:
The use of structural color here overcomes the challenge that the dense, nutritionally valuable anthocyanins make fruits dark and therefore potentially inconspicuous (49). As observed also in Viburnum tinus (16), once overlaid with bloom, darker anthocyanins enhance the chromaticity of the fruit by reducing color mixing. This is also important in maturation (fig. S3): Bloom is present throughout fruit development, displaying a bright UV signal, but only once the bright pigmentary scattering of early ripening stages is removed is the final blue-UV mixed color, due entirely to the bloom structure, visible. Given the other functional benefits of bloom for plant health (40), there is also the possibility that its chromatic visibility could act as an honest signal, displaying an innate high-quality trait. The phenomenon is observed in unrelated cultivated and wild fruits, indicating convergent evolution in a signaling organ, but given the complexity of fruit ecology, behavioral tests would be required to understand whether the coloration enhances frugivore attraction.
If I were to interpret the above statements, it appears that the blue coloration may be a final destination, in which case it may serve as a signal that the fruit may be ready for consumption.
This study may not amount to much, and for many this may be something is otherwise obvious. Nonetheless, it at least provides insights into something that we may not think of too often, and why appearances are not what they all appear to be.
That whitish coating on fruits may serve a purpose, and in fact may serve to alter how we perceive the color of said fruits- how often have you picked up fruit and wondered what that whitish coating is?
If anything, studies such as these help to change how we perceive the world around us and understand that there’s more than meets the eye.
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Zi, J., Yu, X., Li, Y., Hu, X., Xu, C., Wang, X., Liu, X., & Fu, R. (2003). Coloration strategies in peacock feathers. Proceedings of the National Academy of Sciences of the United States of America, 100(22), 12576–12578. https://doi.org/10.1073/pnas.2133313100
Giraldo, M. A., Yoshioka, S., Liu, C., & Stavenga, D. G. (2016). Coloration mechanisms and phylogeny of Morpho butterflies. The Journal of experimental biology, 219(Pt 24), 3936–3944. https://doi.org/10.1242/jeb.148726
Middleton, R., Tunstad, S. A., Knapp, A., Winters, S., McCallum, S., & Whitney, H. (2024). Self-assembled, disordered structural color from fruit wax bloom. Science advances, 10(6), eadk4219. https://doi.org/10.1126/sciadv.adk4219