Three experiments demonstrate that with 8 c/deg. gratings colour selectivity in the tilt illusion exists despite different methods of measurement, different surround inspection orientations and different sized centre test stimuli. Colour selectivity was, however, absent with 3.3 c/deg. gratings. A fourth experiment showed a similar absence of colour selectivity in the tilt aftereffect with 3.3 c/deg. inspection and test gratings. These results resolve a conflict in the literature and further indicate that low spatial frequency orientation-selective cells are sensitive only to luminance contrast whereas those responsive to higher spatial frequencies are also sensitive to colour contrast.