If there’s one color that almost universally symbolizes nature, it’s green. The reason is straightforward: green is the dominant color in the plant world. While other colors emerge when we consider fruits and flowers, blue remains a noticeable exception. So, where is all the blue?
It’s not that blue doesn’t exist in plants at all. Some garden favorites, such as hydrangeas, cornflowers, and delphiniums, offer true blue varieties. Rare species like the sapphire tower plant even flaunt their blue shades proudly. Some sea holly species (Eryngium) take it further with electric blue stems. However, true blue is still hard to find, and many supposed blue plants are actually purple. Even blueberries don’t contain any blue pigment. So, why is blue such a rare color among plants?
Plants rely on light to generate the energy they need through photosynthesis. Within the visible light spectrum, blue light is the most energetic, making it crucial for plants to absorb. Pigments in plants appear as the color they reflect rather than absorb. Therefore, if a plant were blue, it would reflect blue light instead of absorbing its energy, which is not ideal for growth. This is why most plants are green; they contain chlorophyll, which reflects green light, giving the natural world its lush appearance.
However, when it comes to flowers, blue can be advantageous. It helps plants stand out and attract pollinators in a sea of yellows and reds. A recent study found that blue flowers are closely linked to one particular pollinator: bees. According to Dr. Adrian Dyer, “Bees have photoreceptors sensitive to ultraviolet, blue, and green wavelengths, and they also show a preference for ‘bluish’ colors.” While the reason behind bees’ preference for blue flowers remains unclear, the study’s data revealed that blue pigments appear mainly in flowers that rely on bee pollination.
Despite the benefits, creating blue pigment is challenging for plants. Humans have also struggled with this, especially when trying to produce blue dyes. Because of blue’s rarity in nature, early civilizations had to create synthetic pigments, like Egyptian Blue. Even today, new blue pigments are highly valued, as demonstrated by a team at Oregon State University, who accidentally synthesized a vibrant blue compound named YInMn blue in 2009.
The pigments responsible for the few blue flowers that do exist are called anthocyanins. Over 600 types of anthocyanins have been identified, classified into six groups. The presence of certain anthocyanins in a plant contributes to its color, but they can also interact with metals, other pigments, and even the surrounding pH to produce various hues, including blue.
While creating a true blue color is difficult, there’s another factor to consider. Although we might not see much blue in the natural world, the species that matter most to these plants—like bees—perceive color differently than we do.
As Dyer and his team explained, “While humans view blue as a less frequently evolved color in nature, to understand signaling, it is essential to employ models of biologically relevant observers.” In other words, what we see isn’t as important as what bees see.
So, while blue might seem rare to our eyes, there are more blue flowers out there than we realize. Fortunately for these plants, human vision isn’t their primary concern—it’s all about attracting the bees.