Plagarized from an article on Kelly-Moore Paint's website
How to select interior color
Light colors will help lighten a dark or poorly-lighted room, and provide a psychological lift. Light colors also make walls and ceilings appear to be further away, and can be used to make small rooms appear larger and more open.
Dark colors can give a room a dramatic look, and create a sense of intimacy. They can also make walls and ceilings appear to be closer, and can be used to make a large room appear smaller and more cozy.
Bright, vibrant colors will give the room a cheerful feel, and a sense of excitement.
Reds, yellows and oranges are warm colors. When these colors are used in a room, they make the walls appear closer, creating the illusion of a smaller room.
Violets, blues and greens are cool colors. When these colors are used in a room, they make the walls appear farther away, creating the illusion of a larger room.
Tans, greys, and off-whites tend not to attract attention, and can be used to create a restful, relaxing atmosphere. They are also easier to coordinate with other colors in the room.
For long, narrow rooms, paint the shorter walls a darker color. This will make these walls appear closer together, so the room will seem less like a tunnel.
For square rooms, paint one wall a different color, preferably the wall first seen when entering the room. This will give the room a more dramatic look and make it seem less 'boxy’.
How to select exterior color
When selecting exterior paint colors, take the fixed colors into account (like the roof, brick, stonework or any stained wood), and make sure all the colors look good together.
Light colors will make a small house seem larger, and dark colors will make a large house seem smaller.
A large, boxy house can be broken up by using a trim color that contrasts the body color.
A small house will appear larger if the trim is painted the same color as the body of the house.
Light colors will help keep a home cooler in warmer climates, because they absorb less heat. Dark colors will help keep a home warmer in cooler climates, because they absorb more heat.
Because light colored paint films absorb less heat, they will generally last longer than darker colored paint films.
Some communities have restrictions on what colors can be used on house exteriors, so check this out before you make your choice.