Artist Concetta Antico says she sees subtle red, blue and green hues within ordinary shadows that her students did not perceive. Genetic testing later indicated that she may have tetrachromacy, a visual trait linked to the possible presence of a fourth type of cone cell in addition to the three cone types found in most people. In theory, the additional cell could send a wider range of signals to the brain and support finer color discrimination.

Research cited from Newcastle University’s tetrachromacy project suggests that about 12 percent of women may carry genetic traits associated with producing four cone types, although rates can differ among populations. Having the gene or an extra cone cell does not by itself establish that someone sees more colors. Dr Kimberly A. Jameson of UC Irvine says functional tetrachromacy refers to demonstrably enhanced color discrimination, but proving it is difficult.

Scientists disagree on whether tetrachromats perceive entirely new colors or simply distinguish more subtle differences within familiar colors. Online tests cannot reliably diagnose the condition because most screens use only red, green and blue channels. Experts say genetic testing and laboratory-based assessments are comparatively more reliable, while the process through which retinal tetrachromacy becomes functional tetrachromacy remains incompletely understood.