when we use a smart phone to picture someone, it gets red, green and blue rgb values on every pixel. actually converting camera rgb values into something scientifically meaningful is very difficult. we used some relatively simple machine learning algorithms, but to do that we need to have lots of examples of images of people, and then their true skin colour, which we measure in the laboratory, and based on those two sets of data we can learn relationships between the two. what were your key findings in the process of creating the index? the main way in which people's skin colour varies is in terms of hue and lightness, but we actually analyse quite a lot of people who had very very dark skin in our process. we didn't find anybody with a blue undertone, if you like, so we tend to think that is probably a myth. the web—based tool and the index provide a framework for detecting up to 10,000