Rachel McAdams is a great example of how your hair colour can completely change your look. She is most familiar to me for her role as Regina George in 'Mean Girls' but I almost don't recognise her when she has dark hair. She has starred in many films since Mean Girls (of course) and is now out to promote The Lucky Ones.

She spoke to the New York Times about her ever changing hair colour:

It’s a compulsion: I’m always changing parts of me. Even when I was young, I wanted to change my hair color. I was so determined that I dyed my hair with Kool-Aid. You dunk your head in a bowl of red Kool-Aid for four hours, and it comes out apricot. Not that pretty, but it is still transforming. Even my handwriting changes regularly. [She laughs.] They say that only happens with sociopaths, so maybe I’m crazy.

I too am a big fan of changing my hair colour. You wouldn't wear the same outfit every day so why stick with the same hair colour! Do you like to change your hair colour?
Source