Blonde Transformation

I took one of my friends blonde, she always thought she could never be blonde and look good. Well I told her when I first started doing her hair that I'd get her blonde one day. As per usual I always get my way. She won't be staying this blonde colour for long, she wants to go teal coloured soon, but I thought I'd share this little tid bi with you guys. Any colour is possible, it just depends on the tone you pick out :)
Are there colours out there that you think you can't pull off?