The technology works by running a current through a special polymer applied to the vehicle before painting. This polymer contains particles of 'paramagnetic' iron oxide. With the application of an electric current, the spacing of the oxide's crystals is adjusted, affecting their level of light reflection and thus our colour perception.
Cars, being rather conductive metal objects, are therefore the perfect medium for such a technology, with the small current maintaining a particular colour. However, with no current, such as when the car is turned off, the paint would return to its default colour of white, making finding the car after a shopping trip a tricky business indeed.
In a way we would return to the days of Henry Ford, when all cars were black. Of course, they'd only be white until you hit the ignition!