When stimuli are made sufficiently small, colour-normal individuals report a loss in hue perception, similar to tritanopia. This effect is referred to as small-field tritanopia. The interaction between small-field tritanopia and the rods working in scotopic vision has not been clarified. In this study, the problem is investigated by freely adjusting the hue, lightness, and saturation of the test stimulus to match the colour of the reference stimulus by observers. Three colours on the blackbody radiation trajectory with colour temperatures of 3500K, 5400K, and 11600K were used as reference colours. Each stimulus subtended a diameter of 6' and 10.8'. The 5400K and 11600K stimuli were distributed diagonally from the lower left to the upper right of each reference stimulus in the CIE 1976 uv uniform chromaticity scale diagram. The distribution was similar to those of tritanopia. For the 3500K stimulus, the result did not show the influence of small-field tritanopia.