Until recently, descriptions of peripheral colour perception have been largely qualitative. The present paper reports a quantitative determination of the colours of peripherally presented lights, in which a foveal mixture field is used for comparison. Observations were made under dark adaptation conditions by two observers. The colour changes are analysed in terms of hue and saturation. In addition, spectral sensitivity curves are derived from the colour-matching data. Some subsidiary experiments are reported which indicate effects due to light adaptation, test luminance and exposure time. The results indicate a progressive deterioration in colour perception with distance from the fovea: tending, under the conditions of the experiment, to dichromatism at 25°-30° and to monochromatism at 40°–50°. The roles of (a) rod vision, (b) the fusion of nerve pathways, and (c) the depletion of the cone population are discussed.