Um.  It's been known for decades that if you put a rat on an artificially
constructed diet deficient in PABA, one of the symptoms is reduced
ability to produce hair pigment.  I don't believe it's possible to come
up with a diet composed of stuff normally regarded as food that would
cause gray hair from PABA deficiency without first causing a bunch of more
serious deficiency diseases like beri-beri or pellagra.

If you start developing white hair at what you regard as an early age,
it's almost certainly due to your genes, not your diet, and supporting
"Vitamin Research Products" in their quest for profits is not going to
make your hair return to its original color.

It's just like all those quack cures for male pattern baldness -- just
because ringworm and some other conditions can cause baldness, doesn't
mean that the treatments for those conditions will grow a thick head of
hair on somebody with the genes, age and testosterone level to manifest
male pattern baldness.

Ditto, kwashiorkor, the disease of protein deficiency, cause reddening
of normally dark hair, among other symptoms.  This doesn't mean that
somebody who is naturally red haired will become a brunette if he
eats more protein.

Don't believe everything vendors tell you about what they want to sell.