Abstract

When participants are asked to make settings of the colour white in a dark room, the settings vary to a surprisingly large degree in a blue-yellow colour direction. The nature this uncertainty may provide a clue to what it is that causes us to perceive a stimulus as white. I will present the results of a series of experiments that aimed to test the hypothesis that white may be perceived as any stimulus that could plausibly arise from the combination of a surface reflecting all wavelengths of light equally, and a natural illuminant. I will discuss how far the evidence favours this or other hypotheses for what is white.