Are there any references to if hair dyes existed in Europe in the middle ages, and if so how they worked? This last week on the TV show Game of Thrones, one character dyed her hair to blend in, and it made me curious if this was a thing people might have thought of at the time as a disguise.
Looking around in this subreddit, I found a thread that mentions that hair dyes have existed for some time, but has no actual information about how they went about it.
Henna has been used for thousands of years to dye hair, particularly in parts of Asia and Africa, including Egypt. Henna's use is limited to just shades of red, however. I believe it was also later used in Europe - for much of early European history, such as in ancient Rome, red hair was not considered a beauty ideal so it would not have been used. People actually still use henna as an organic option for hair dye, although you're not likely to find it in a traditional salon.
Source: I received a BA in classical studies (I'll also add I'm a redhead and so have a particular interest in the history of perceptions of red hair)
I cannot say for certain about late Middle Ages, but in Early MA, we know that Vikings would dye (ro rather bleach) their hair, and there is noreason to beleive that the art of doing that would die out.
Plus, the techniques required to dye/bleach wool and the dyes for that were know since early antiquity, and human hair abosrd the same chemicals as wool.