edit: not really low brix but mineral deficient
This may not explain why one gets gray hair or why one day one gray hair will appear right next to a dark one, but it does appear that the lack of minerals in a hair does express a lack color!
It also suggests that mineral deficiencies are related to aging and graying!
Abstract;An investigation of the metal concentrations of potassium, sodium, calcium, magnesium, copper, zinc, manganese and iron in the black and gray hairs of the same person in Taiwan was performed using atomic absorption spectroscopy (AAS). The flame modus of AAS was employed to determine the concentrations of trace and mineral elements. The results of trace element and mineral element concentration determinations were evaluated by statistical analysis using the t-test for comparison of significant differences between black and gray hairs of the same person in the same region of the head. Our findings revealed that the concentrations of potassium, sodium, calcium, magnesium, copper, zinc, manganese and iron in gray hairs were lower than those in black hairs. Concentrations of manganese, copper, magnesium, calcium and sodium showed significant differences between the two kinds of hairs (p < 0.05). On the contrary, no significant differences were noted in zinc, iron, and potassium (p > 0.05). Our experiment gives direct evidence to suggest that reduction of hair trace element and mineral element concentrations may be one of the factors associated with hair graying or aging. Manganese, copper, magnesium, calcium and sodium obviously have .greater effects on the hair color and aging. (author abst.)