The present invention is a method for assessment of color processing mechanism in the human brain using cerebral blood flow velocity monitoring, specifically transcranial Doppler ultrasound. The method including steps of transluminating color discs from a light source of a specific color temperature, which act on the visual pathways and color centers to alter mean blood flow velocity in the cerebral arteries. The mean flow velocity is analyzed and using Fourier computation to calculate spectral density estimates. Opponent mechanism in the cortical and subcortical regions determined as opposing tendency for short wavelength versus medium wavelength or for medium wavelength versus long wavelength colors. The method is applied for diagnosis, and treatment of variety of conditions.