Not in the obvious way of course

I have a photo with a white background, and I need to make it a very dark background... but the photo has a woman with loads of strands of hair and although i can change the colour of most of it with paint bucket/magic wand or something, it's really hard around the hair area.

I thought you could replace colour with adjustments - colour - replace colour or something but it doesn't seem to work.. any tips?

Thanks.