Chromophore

Common examples include retinal (used in the eye to detect light), various food colorings, fabric dyes (azo compounds), pH indicators, lycopene, β-carotene, and anthocyanins.

Lengthening or extending a conjugated system with more unsaturated (multiple) bonds in a molecule will tend to shift absorption to longer wavelengths.

The nature of the central metal can also influence the absorption spectrum of the metal-macrocycle complex or properties such as excited state lifetime.

Because of their limited extent, the aromatic rings only absorb light in the ultraviolet region, and so the compound appears colorless in the 0-8 pH range.

However, as the pH increases beyond 8.2, that central carbon becomes part of a double bond becoming sp2 hybridized and leaving a p orbital to overlap with the π-bonding in the rings.

This makes the three rings conjugate together to form an extended chromophore absorbing longer wavelength visible light to show a fuchsia color.

Leaves change color in the fall because their chromophores ( chlorophyll molecules) break down and stop absorbing red and blue light. [ 1 ]
Healthy plants are perceived as green because chlorophyll absorbs mainly the blue and red wavelengths but green light, reflected by plant structures like cell walls, is less absorbed. [ 2 ]
The eleven conjugated double bonds that form the chromophore of the β-carotene molecule are highlighted in red.
The porphyrin moieties in our red blood cells, whose primary function is to bind iron atoms which capture oxygen, result in the heme chromophores which give human blood its red color. Heme is degraded by the body into biliverdin (which gives bruises their blue-green color), which in turn is degraded into bilirubin (which gives patients with jaundice a yellow skin tone).
In the mammalian eye , the molecule retinal is a conjugated chromophore . Retinal begins as 11-cis-retinal, which, upon capturing a photon γ (light) of the correct wavelength, straightens out into all-trans-retinal which pushes against an opsin protein in the retina , which triggers a chemical signaling cascade which results in perception of light or images by the brain.