“We colour her hair every Monday, before we film The Voice. Gwen’s an Italian girl with wavy brown hair — if you look at the video for Cool , we did her in her natural shade, maybe a little darker — so I developed a high lift formula for her. I learned that I could get to a place of achieving the blond that I want, and the quality of hair that we need and want, by using a new product, as opposed to just bleach. People are like 'that's not natural' and I say, ‘Of course it is — it's supernatural’."