I did some research today,

http://www.colorbond.com/home/residential/roofing/thermal-efficiency

http://www.steelroofing.com/energy_efficient_choice.pdf

http://preengineeredsteelbuildings.net/news-society/energy-efficient-color-options-for-pre-engineered-steel-buildings/

http://www.resene.co.nz/homeown/probsolv/prob10.htm

Here's some info:

• Lighter colours radiate less heat during the summer.
• The sun is higher in the sky in summer.
• If your home faces true north, it will receive more sun.
• Eave-overhangs will prevent direct sunlight exposure in summer.
• "Cool" paint-based sun reflecting pigments act to reflect the infrared radiation.
• This means less solar energy is transferred throughout the home.
• Less heat, means less energy to cool and thus, reducing cooling costs.
• Reflectance is the amount of light reflected compared to the amount of light that falls on the given surface.
• Dark, matt and/or textured surfaces absorb a lot of light and have low light reflectance values. Light, glossy and/or smooth surfaces reflect most of the light that falls on them and have high light reflectance values.
• The higher the reflectance value, the less heat is transferred, home remains cooler.