young-helmholtz theory \ˈyəŋˈhel]mˌhōlts, -ˈheu̇]-\noun Usage: usually capitalized Y&H Etymology: Thomas Young died 1829 English physician and physicist and Hermann L. F. von Helmholtz died 1894 German physicist : a theory in color vision: the eye has three separate elements each of which is stimulated by a different primary color