Unsupervised alignment reveals shared but locally refined colour qualia structure from toddlerhood to adulthood

Whether subjective colour experience (e.g., experience of 'red') is shared across children and adults remains a foundational question in developmental psychology and consciousness research. To test this, we compared the relational structures of their colour experiences and identified the mapping that best preserved these structures. Using pairwise similarity judgements for 13 basic colours, we applied Gromov Wasserstein optimal transport (GWOT), an unsupervised method requiring no prespecified stimulus experience correspondence to compare toddlers, preschool children, and adults. Preschoolers' and adults' group-averaged structures perfectly aligned, whereas toddlers' structure did not fully align with either older group. However, removing specific colours, particularly those with relatively late acquired linguistic boundaries, such as light blue-restored near-perfect alignment. Moreover, toddlers with greater colour-word knowledge showed closer correspondence with the adult similarity structure. These findings suggest that the global relational geometry of colour experience is largely established by toddlerhood, with limited local differences linked to colour-language acquisition.