Ive been on Armour for 3 months, My mother has been on it for 20 years, and I have not experienced this, nor heard of this happening to anyone.
I've never heard of that as a symptom of hypo or a side effect of Armour, either. Stress can change hair color. So can vitamin deficiencies and diet. I don't know how old you are, but hair typically darkens before it turns gray as well.