Abstract: A colorimeter is provided in which a measuring pipe diverts a sample of a substance off of a production line into a measuring chamber. A series of cut-off valves control the quantity of the sample accumulated in the measurement zone to ensure sufficient amount for analysis. An optical head having three concentrically aligned light projectors projects light onto the sample. Light reflected off the sample, the wavelength of which indicates the sample's color, is collected by an optical collection system and sent to a color analyzer for comparison with a predetermined color. The measurement chamber is provided with temperature, humidity and level sensors to account for shifts in wavelength due to these parameters.