Chromophore
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A chromophore is the part of a molecule responsible for its color. The word is derived from Ancient Greek χρῶμᾰ 'color' and -φόρος 'carrier of'. The color that is seen by our eyes is that of the light
Leaves change color in the fall because their chromophores (chlorophyll molecules) break down and stop absorbing red and blue light.
Opsin
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Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become retinylidene proteins, but are usu
Three-dimensional structure of cattle rhodopsin. The seven transmembrane domains are shown in varying colors. The chromophore is shown in red.
The retinal molecule inside an opsin protein absorbs a photon of light. Absorption of the photon causes retinal to change from its 11-cis-retinal isomer into its all-trans-retinal isomer. This change in shape of retinal pushes against the outer opsin protein to begin a signal cascade, which may eventually result in chemical signaling being sent to the brain as visual perception. The retinal is re-loaded by the body so that signaling can happen again.