I think this topic is like many things. In and of itself, it's not a bad thing, but it can easily be made into something bad. I think many women take a wrong approach to such things. I've known (and dated) women who won't leave the house without doing hair and makeup, for example. This shows me their motivations are based in thinking they can't look good without it, and need to seek that approval of others. This mentality is common and a large reason why women do things like this, whether its hair color, or whatever else.
Not to say i'm against these things. Just wish women had more of an attitude of i do this because i enjoy it' rather than 'i need to do this'.
in the bible hmm there is a chapter abt tresses and gold on hair , but it doesn't talk abt coloring hair , and wearing jewels