His radio show has great information but he is heavy-handed with recommending his own products, so you are fore-warned.
Also-- if you look at the product catalog there of Max Stress B-- you will see the product that I take. It is a good B-vitamin and I only use 1/2 tsp a day.
Dr. Marshall clearly states, however, that grey hair in younger adults is due, usually, to B-vitamin deficiencies. However, in older adults the stem cell reserves are begginning to diminish. From the research, the scientists are aware that greying reflects loss of stem cell activity. (one of the stem cell reserves are believed to be in the head region)
He has another product called Gold-360 which helps to maintain and regenerate the stem cells. I know that Dr. Marshall had a head of snow-white hair (he is in his 60s) and now his hair is slowly getting a black luster back to it.
So I am saying that I don't know if your grey hair is due to B-vitamins.