Some offer color-matching software. For instance, Benjamin Moore dealers will also scan a photo of your house and let you experiment with color on a computer screen. Or you can choose a house from the program that looks like yours. Whichever method you use, remember that your roof and landscaping, along with the other houses on the street, won't change. So consider these permanent colors when making your selection.
Dark colors absorb heat and are more likely to suffer from moisture problems.
Even the best exterior paint can fail if it's applied incorrectly. Always use a primer when painting any untreated surface to seal it off and to provide a base for topcoats to stick to. Water-based primers are a good choice if knots aren't an issue. Water-based paints are compatible with both types of primer. When repainting, prime only when necessary.