My mother had been using Garnier hair color (to cover her greys) for 3-4 years. There were no issues with the product for a long time... But after some 2 yrs of using the product regularly (monthly once) she started getting white patches all over her skin, specially on her arms and back. Initially we considered it to be some kind of Vitamin deficiency which seemed to be a common thing among women of her age (50-60). She even consulted some dermatologists who could not suggest what could be wrong. This went on for say an year, during this time my mother herself noticed that the white patches were reducing when she did not apply hair color for a long time (when the interval between color application increased, the patches were getting better)...
Now for the past one year, she has completely stopped using Garnier (shifted to a high end brand) and the patches are completely gone !!! Later we also happened to talk to a relative of ours who also had the same issue with Garnier hair color, but luckily her doctor had detected the issue.
So please be very cautious while choosing hair color.There may be side effects which will not show up for a long time, but may surface in some indirect form after a while. Hope it helps in case you or anyone you know are facing similar issues.....
Have a good day :-)