Twins and odd‐ones‐out: a twin study of genetic contributions to variability in personal colour space

BACKGROUND: Individuals differ in the biological substrate of vision, often as a result of genetic differences. There are also subtle variations within the normal population in aspects of colour behaviour (for example, colour naming and unique-hue judgements) but it is surprisingly hard to connect these to the genetic variation. Perceptions of inter-colour similarities (and variations in the structure of colour space, reconstructed from them) may show a closer link to the biological basis of vision. METHODS: To quantify the spectrum of variation, each subject used caps from the D-15 panel test to make 70 odd-one-out triad judgements. Analysis yielded the parameters of individual observers' colour structure: specifically, the weights they placed on the axes of a standard colour space. Similarities between 19 pairs of monozygotic twins and between 16 pairs of dizygotic twins were compared. RESULTS: Monozygotic pairs were significantly more concordant than dizygotic or unrelated pairs. DISCUSSION: The procedure provides sufficiently precise measurements to replicate earlier findings from more complex, time-consuming methods. By extension to other family relationships, the triadic procedure can clarify the genetic contribution. Weighting of colour axes is an important form of variation among normal individuals, with a contribution to these weights from genetic factors.