The sweep of colours shows minute variations in the Earths gravitational field. If you were to fly over the red areas, you would be tugged ever so slightly downwards; the blues mark regions where the planets attraction is much weaker. These gravity anomalies, as they are known, are imperceptible to the human senses, and so the scientists have wrapped the data on to a sphere and exaggerated the highs and lows.
http://news.bbc.co.uk/2/hi/science/nature/3093927.stm
