I'm not 100% sure, but I saw the advert this morning. I have looked all over the internet :-) but haven't come up with anything concrete. I think though, it sounds very much like an American singer called Joanna Newsom. The style is very much the same. I love listening to Joanna's music and I love the song true colours... so if anyone has the definitive answer... please let us know :-)
Jen x