And, unfortunately, the dark dyes have been linked to non-Hodgkins lymphoma. I often wonder if that is what caused Jackie Kennedy's cancer.
"What problems can hair dyes cause?
Some of the problems people have had from using hair dyes are:
hair loss
burning
redness
itchy or raw skin
swelling in the face
trouble breathing"
http://www.fda.gov/forconsumers/byaudience/forwomen/ucm118527.htm
That's funny, I had my hair dyed yesterday and the same thing happened - the white hairs just weren't coloured properly! It's the same dye they have used in the past so it must be connected with the low thyroid situation.
I asked the hairdresser about hair damage, and he said adding colour does not damage your hair, but lightening it with any beaching agents does. So I think that means highlights might be best avoided.
What are the actual results of your thyroid tests? Please post them, along with the reference ranges, which vary lab to lab, so must come from your own report.
If there's an underlying cause of hair damage (such as thyroid issues), hair dye can do further damage.
I would keep coloring my hair. Damage would be caused by the thyroid problem, not the dye.