Eyes wide open..

Yesterday's damselfly-blip's eyes made me think of the variety of eyes of invertebrates, so I decided to make a collage of some of the insects and spiders I have photographed recently to compare them..(unfortunately I always download the photos in low resolution on my phone, so the quality is not as good as if I had worked from the computer). Then I searched the scientific databases, looking for a simple answer to the question what makes the difference, but the world of the invertebrate eye colour is far more complicated than I imagined, full of jargon, pathways and hypothesis, so I'll just touch the surface.

Insects have three types of eyes, simple, apposition compound, and superposition compound eye and the colour can vary from black, red, blue, yellow, green, brown, compound etc. determined by the absorption spectra of the screening pigments in the rhabdom. Most insect eyes contain black screening pigments (the simplest and most "economical" option) which prevent stray light to produce background noise in the photoreceptors, many insects have red eyes which permit stray light to photochemically restore photo-converted visual pigments and the yellow pigment granules act like the pupils of the eye which control the light sensitivity and adjust it accordingly...but often the colours have the main function of displaying a certain pattern, just like its body colour! ...but maybe that is just an explanation given for the more difficult to understand relationships!
And in case you were wondering, the pigments for eye and body colour are either synthesized by the insect itself or absorbed from the antioxidative carotenoids and flavonoids of their host plants. So their diet can be fundamental for the vision, just as for us!