No surprise* that a light coloured car will be cooler than a dark coloured one. Interesting, though, to see it quantified in terms of air conditioning & fuel consumption.
* No surprise to anyone other than Chevrolet – the roof of every Volt is black!!?? In Europe the principle seems to have been understood – the roof of the Ampera (European version of the Volt) is the same colour as the rest of the body.