tl;dr of below paragraphs: I think it's better to have multiple tags if the color is "subjective", rather than having just one and it being different from what some people would expect.
I know it's a 2 year old comment, but I don't see a problem with there being 2 color tags for the same thing. The hair is not black, it's more like a purpleish brown, but it's dark enough for it to appear as "black" when searching for black hair pictures.
Likewise, sometimes what some people consider "red eyes" might actually be orange or brown, and so on. Or even, pickier people might want to differentiate between purple and lavender or other more specific colors, so it's good to have options.
This is one of those cases where the color might have a different name depending on who you ask. I doubt someone tagged it purple by mistake. Brown, black, purple pushing it a bit, those 3 are okay here imo. Just as those thousands of pictures where the hair is red, pink, purple AND magenta.