Because you CAN use other odd colors to dye hair. So long as you have access to the appropriate colors needed, it can be done. As I stated before, regions were limited by what they had, but they were available. In the game we’re not limited to a few colors because we can traverse the map. Also, we’ve concluded the idea probably shouldn’t be a Nergal permanent dye method, but rather more likely on the dyers bench as a temporary method like warpaints. This would maintain the idea that it’s only temporary dying. So in the end, arguing with silly non-lore ideas as examples for it’s ridiculousness is a bit excessive and not even relevant at this point.