What is the principle of bromocresol green indicator color?

As an acid-base indicator, the basic principle is the same, but the range of color change is different. The basic principle is that the change of molecular and ion yoke system leads to different absorption spectra, which leads to different color development. In different PH media, the concentration ratio of molecular indicator and ionic indicator can not be the same, so it shows the dominant concentration color. Bromocresol green is a commonly used acid-base indicator in non-aqueous titration (prepared in anhydrous ethanol). Yellow at pH=3.8, blue-green at pH=5.4, and obvious discoloration at pH=4.5.