The process you refer to is called colorimetric analysis. It is an often used analytical method and many colorimetric tests have been developed that reveal the presence target substances with a sensitivity down to the parts per million level. Such tests are key tools in precision chemical manufacture, forensic science and the purification of water supplies.
Dr. saab ji, During boron estimation: yellow color was developed due to complex formation between boron and indicator and was directly related to boron content, Standard curve was prepared using known concentration of boron. is it correct? Importance of color? I need your valuable suggestions.