We can not say much more about the detailed mechanisms of transducing light into bioelectrical signals. A key requirement in the chemistry of vision is that metarhodopsin, or the bleached pigment of vertebrates, must be reconverted to rhodopsins. In the eyes of vertebrates, this regeneration is the product of a complex biochemical pathway. The pathway involves isomerization back to the 11-cis configuration and assembly with the opsins. Again, invertebrates differ from vertebrates on this aspect of photochemistry.
Light is absorbed by rhodopsin and metarhodopsin in invertebrates.
Absorption of light transforms metarhodopsin back to rhodopsin. The pigments exist in two stable conformations, and light causes them to switch back and fro from one state to the other. This regeneration is essential because conformational changes in rhodopsin, but not in metarhopsin, leads to phototransduction. Experiments on insect behavior indicate that many insect species can distinguish colors. Color vision depends on the ability to discriminate between light of different wavelengths.