Bad idea, but it gives me another. One effect of alchemical potions could be to change hair colour, perhaps temporarily, perhaps permanently. Due to the nature of alchemy, this would generally be random and not purposefully sought after, and the duration of the effect wouldn't be clear immediately. Knowledge of how to produce the potion and the potions themselves could be spread, though. It might also appear as a side effect of a concoction with other effects, which could mean unexpected hair colours might have significant implications about the imbiber. Some of these effects might be more dominant than others and override them, and some might even combine to result in rare shades no one potion could ever produce.
And some potions might cause the user to entirely lose all their hair, which could make it difficult or impossible for them to find any other hair-altering potions. So they might need more test subjects, and skill at fast-talking when they're dissatisfied with the results as well.
I like how the raven black hair colour turned out. Haven't seen someone using the white one yet.