Insects produce their amazing array of colours in two different ways. The first is through chemical pigments. The other, and I think more interesting way, is through bending light. These colours result from light interacting with the physical structure of the surface. These structures absorb or scatter light and allow the insects to create a rainbow of colours without having to make pigments. The colour system works because of a physical principle, refraction. Periodic, regular repeats in the structure allow it to send specific colours back into nature.
Brilliant white may be used as highlights by some species (often with ultra violet undertones), but few insects live their lives as bright-white beings. However, the Cyphochilus beetle never read the rule book. It creates its bright-white refractive coloration with an unusual trick too. Instead of an ordered array of scales sending a particular colour back into the world, it has an irregular array. This random network sends out all the visible wavelengths (and probably others), and hence we perceive it as white!
Why the white? Not known. Possibly to attract mates Possibly to regulate heat. Possibly to blend into the background of the fungus they often visit. No matter the reason, this refraction tech has the potential to displace many of the white pigments, such as titanium dioxide, that have potential carcinogenic properties.