Grue-type errors on traffic light colour-name responses

‘Why do the Japanese call a green light signal blue?’ This simple question has been the subject of numerous media articles. One of the most relevant studies on this question is the finding of colour-name responses. Using the findings of cognitive linguistics based on colour vocabulary and grammatical structures as a basis, this study experimentally tests how differences in linguistic systems and vocabulary affect the cognitive processes of Japanese people in the form of Grue typology in traffic lights. The subjects were 195 university students in the 2020 group (141 valid responses) and 143 students in the 2023 group (104 valid responses), who were interviewed prior to the class through an online assignment form. They were presented with visual stimuli that reminded them of either of the two types of traffic lights with instructions only to “enter/answer the colours that go into each of the circles”, and respond with no other information given. The results showed that in both year groups, significant differences were detected between group B and the other two, while no significant differences were detected between groups R and Y. Among traffic lights, the hue of the caution signal (yellow) is slightly reddish-yellow, and discrepancies between colour perception and the actual signal name can occur for both blue and yellow lights. However, none of the yellow signals were misnamed, even with the slightly reddish-yellow tint. This can result from a grue-type error that occurs between the socially shared semantic code ‘blue light’ and green as perceptual cues.