To be healthy we should eat food with variety of colours. But there is one exception, blue colour. Blue coloured food is so rare—and if there is blue food on the plate, I guess it will be unappetizing to eat. How about blueberry? Blueberry is yummy, isn’t it? The thing is blueberry is not actually blue—yes the outside is blue—but the inside is more like purple. In fact, the colour of blueberry is changing depending on the acidity of the environment.
So why does blue is so rare in plants?
Colour in plant comes from pigments. There are two type of pigments come into play in here. The first is carotenoids, which responsible for yellow, orange, and red colour. Carotenoid is the chemical that gives carrot its orange colour. The second pigment is anthocyanins, which responsible for red, purple, and blue colour. These anthocyanins are found from grape to eggplant, noticeably the purple colour.
The common element of both pigment is red. Why red? On the colour spectrum, red is the antagonist of green—the colour of leaves. Hence, if a plant want to make something stand out, red is the obvious choice. And that’s probably the product of evolution.
How about the plant that rich with anthocyanins? Why is it not blue? Most plants that rich with anthocyanins, e.g. grape and eggplant, end up with purple colour. Simply, it’s because the mixture of red and blue produce purple colour. The chemical substances of blue anthocyanins are less stable, thus they usually dominated by other pigments.
Blue is rare in plants, though it is even rarer on animals.
Sure there is a blue butterfly—the blue morpho butterly. However, the blue here is not because of pigments but because of the wings structure. The microscopic structure of these wings show because of their orientation, the light phase of colours other than blue are cancelled out. Hence, only the vibrant blue colour gets into our eyes.
In a nutshell, blue food is rare because blue colour is rare in nature in the first place.