PURPLE. But since this world sucks and people care to much about other people's opinions, let's go with black.
Black fits with almost everything, making it such a magnificent color. Even though it's actually the absence of color and therefor couldn't really be defined as a color.
But who cares anyway.
I naturally have light brown hair, and have had it anywhere from blonde to green , but I dye it dark brown/blackish to match my eyebrows. I prefer dark hair.