Aluminum and steel casings and aluminum, steel, or ABS plastic for backplates are the usual materials. Glass covers are also used in decorative models.
Electro-plating and powder-coating are the standard finishes, available in many colors. These finishes ensure rust and corrosion-resistance in outdoor environments, and also offer scratch-resistance.
Think of these color-combinations for your home:
White or ivory for exterior walls in the white and yellow families of colors. They will require frequent cleaning, though.
Black and dark-colored lights for both light and dark-colored walls. Avoid this finish if you live in a warm environment because they absorb heat.
Neutral colors for dark walls for a good contrast.