Association between synesthetic colors and sensitivity to physical colors changed by type of synesthetic experience in grapheme-color synesthesia

•Grapheme-color synesthetes have superior color discrimination abilities.•Synesthetic and non-synesthetic colors were identified by synesthetic color clusters.•Associator and projector synesthetes showed different color sensitivity.•Implications for color-processing understanding in grapheme-color synesthesia. Grapheme-color synesthesia is a condition in which visual perception of letters induces simultaneous perception of a specific color. Previous studies indicate that grapheme-color synesthetes are more sensitive to physical colors than non-synesthetes. Synesthetic colors are found to be concentrated in multiple regions of the color space, forming “synesthetic color clusters”. The present study investigated whether color sensitivity corresponding to synesthetic color clusters (clustered colors) is higher than color sensitivity that does not correspond to synesthetic color clusters (non-clustered colors). However, we found no difference in the color sensitivity for clustered and non-clustered colors. We also investigated whether the color sensitivity is dependent on the synesthetic experience (associators and projectors). We found that the greater the tendency toward associator characteristics, the greater the sensitivity for clustered colors compared to that for non-clustered colors. Our findings suggest an association between synesthetic colors and physical color sensitivity that is modulated by synesthetic experience.