Instantaneous chemical reactions, either themselves or together with chemical indicators, have previously been used as probes of turbulent micromixing. Both methods obtain statistics of the micromixing from measurement of time mean quantities. The mean reactant concentration, which is the quantity measured in the instantaneous reaction method, is shown here to be the integral with respect to feed concentration ratio of the mean color density, which is the quantity measured in the chemical indicator method. Differentiation of the mean color density gives the scalar probability density while integration gives the mean reactant concentration. Measurements of the color density of bromothymol blue at the centerline of a turbulent jet of base mixing with acid are used as an example.