Auxochrome no relation color
A chromophore is the part of a molecule responsible for its color.
The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum. Visible light that hits the chromophore can thus be absorbed by exciting an electron from its ground state into an excited state.  In biological molecules that serve to capture or detect light energy, the chromophore is the moiety that causes a conformational change in the molecule when hit by light.Auxochrome
An auxochrome is a functional group of atoms attached to the chromophore which modifies the ability of the chromophore to absorb light, altering the wavelength or intensity of the absorption.Halochromism
Halochromism occurs when a substance changes color as the pH changes.  This is a property of pH indicators, whose molecular structure changes upon certain changes in the surrounding pH.  This change in structure affects a chromophore in the pH indicator molecule.  For example, phenolphthalein is a pH indicator whose structure changes as pH changes as shown in the following table:
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