For a pain-color synesthete, a headache might be a dull orange disc and a stubbed toe a spray of white points. The pairings behave like other synesthesias: automatic, specific, stable over time.
Clinically the trait cuts both ways. Some synesthetes find describing pain easier, since they can report color, brightness, and shape where others reach for strained comparisons. Pain scales built on words fit them badly, though, and the literature contains cases where the visual channel communicated severity better than any number out of ten.
The form is rare and mostly documented in case studies rather than large samples.