Research the traditional color schemes if your house will be built in period style. Determine what elements of the historical color choices make sense for your house, lot and neighborhood. Walk the neighborhood and notice the colors of neighbor's homes. Your McMansion shouldn't stick out like a sore thumb on a homogeneous block. And check the homeowner's association color palettes if you live in a community with regulations about exterior paint colors and materials. Your choices may be limited to a preapproved list.
Choose decorative elements like stone facing and roof tiles. Those will affect the rest of the color choices. Consult with the architect about the climate and how frigid winters or glaring summer sun will fade or weather the home's exterior.
Consider a few classic ways to deal with picking colors. Look at monochromatic color schemes that stick to one color with several values, like pale, medium and slate gray. Try a complementary color scheme to make the house "pop." Complementary colors are opposites on the color wheel and provide high contrast, like an apricot-colored home with navy shutters and trim. Triadic colors are three colors equidistant on the color wheel and are a very ornate exterior treatment. They work well on period-style houses such as those with lacy Victorian architecture.
Coordinate the walkways, walls and fences and foliage colors with the color scheme for the home. A blue slate walkway might look terrific with a stone facade and a dark roof but clash with an adobe-colored Spanish colonial.
Get the best paints, most durable finishes and highest quality materials you can afford so the exterior of the home will look new for years to come. And keep paint color numbers, formulas and samples in a safe place to refer to when it's time to repaint and repair.