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> Only some flowers can produce petals that either are blue or look blue. Bumble bees look for them:
> 
> https://www.sciencedaily.com/releases/2017/10/171018132826.htm
> 
> "Latest research has found that several common flower species have nanoscale ridges on the surface of their petals that meddle with light when viewed from certain angles.
> 
> "These nanostructures scatter light particles in the blue to ultraviolet colour spectrum, generating a subtle effect that scientists have christened the 'blue halo'.
> 
> "By manufacturing artificial surfaces that replicated 'blue halos', scientists were able to test the effect on pollinators, in this case foraging bumblebees. They found that bees can see the blue halo, and use it as a signal to locate flowers more efficiently.
> 
> "While the ridges and grooves on a petal surface line up next to each other "like a packet of dry spaghetti," when analysing different flower species the researchers discovered these striations vary greatly in height, width and spacing -- yet all produce a similar 'blue halo' effect.
> 
> "In fact, even on a single petal these light-manipulating structures were found to be surprisingly irregular. This is a phenomenon physicists describe as 'disorder'.
> 
> "The researchers conclude that these "messy" petal nanostructures likely evolved independently many times across flowering plant species, but reached the same luminous outcome that increases visibility to pollinators -- an example of what's known as 'convergent evolution'.
> 
> ***
> 
> "All flowering plants belong to the 'angiosperm' lineage. Researchers analysed some of the earliest diverging plants from this group, and found no halo-producing petal ridges.
> 
> "However, they found several examples of halo-producing petals among the two major flower groups (monocots and eudicots) that emerged during the Cretaceous period over 100 million years ago -- coinciding with the early evolution of flower-visiting insects, in particular nectar-sucking bees.
> 
> "'Our findings suggest the petal ridges that produce 'blue halos' evolved many times across different flower lineages, all converging on this optical signal for pollinators," said Glover.
> 
> ***
> 
> "Previous studies have shown that many species of bee have an innate preference for colours in the violet-blue range. However, plants do not always have the means to produce blue pigments.
> 
> "'Many flowers lack the genetic and biochemical capability to manipulate pigment chemistry in the blue to ultraviolet spectrum," said Vignolini. "The presence of these disordered photonic structures on their petals provides an alternative way to produce signals that attract insects."
> 
> ***
> "'Humans can identify some blue halos -- those emanating from darkly pigmented flowers. For example the 'black' tulip cultivar, known as 'Queen of the night'."
> 
> "'However, we can't distinguish between a yellow flower with a blue halo and one without -- but our study found that bumblebees can," she said."
> 
> Comment: Bees can see what we can't. But bees are needed for pollination and we are not. This is how balance of nature is set up; many little arrangements.