Whether or not colour discrimination is involved in the process of eliciting the landing response of the fly was investigated with rotating linear spiral patterns of different spectral composition. With monochromatic patterns execution of the response depends on the contrast in the pattern: no response occurs within a restricted range of intensity ratios corresponding with low pattern contrast. With dichromatic patterns execution of the response depends on the intensities of the two spectral components (which each dominate half the pattern). No response occurs within a restricted range of intensity ratios; this range characteristically depends on the spectral wavelengths in the pattern. The mean values of these ranges are used to determine a spectral sensitivity distribution of the landing response. In an alternative procedure the spectral sensitivity was obtained from threshold intensities of a high contrast spiral pattern superimposed on a constant background. The spectra obtained by the two methods are very similar broad-band curves with peaks in the UV and in the blue-green. At the intermediate and low intensity range the contrast thresholds are slightly dependent on the intensity. Taken together the results suggest that with moving stimuli colour discrimination is absent in the landing response pathway. What is processed are just contrast differences determined by intensity and spectral wavelength.