Individual-to-individual mapping of color similarity structures: Is my "red" relationally your "red"?

Is my "red" the same as your "red"? Although we cannot directly test whether two individuals' experiences (qualia) are identical, we reframe this question as an empirical one: whether my "red" is relationally your "red". We addressed this question by finding the best possible mappings between color similarity structures across individuals, without using color labels. We collected a complete set of similarity judgments across 93 colors from each of 11 participants and compared their structures. These comparisons revealed two groups of four participants in this sample whose structures aligned robustly within each group: the best possible mappings matched the same color stimuli, such as my "red" to your "red". Between groups, however, the best mappings did not match the same stimuli. The remaining participants showed structural variations that did not fit either group. This framework opens a path to classifying diverse color experiences through their relational structures.