Roof tiles that change colour with temperature have been developed by a team of MIT graduates

The tiles turn white when it’s hot and black when it’s cold to absorb more sunlight.

In white state they reflect 80% of sunlight; in black 30%. The tiles use a commercial polymer in a water solution between layers of glass and plastic with a dark layer at the back.

When the temperature falls the polymer stays dissolved and the black backing shows through. When the temperature rises the polymer condenses to form tiny droplets which scatter light and produce a white surface.

Source

Building Sustainable Design