An odor-color synesthete smells coffee and sees a specific brown-gold, or cut grass and sees a sharp green that is not simply the memory of lawns. As always the test is consistency: genuine pairings survive months between retests.
The form intrigues researchers because everyone shows weak, statistically reliable smell-color intuitions (most people call lemon scent yellow), a phenomenon filed under cross-modal correspondence. The synesthetic version differs in being specific and perceptual rather than a loose association, and the two together suggest the trait amplifies wiring everyone shares.