Whenever you are deciding on a paint color, it's important to consider other colors within the palette and the general style and feel you wish to create in the space. When painting the exterior door of a brick house, your primary constraint will be the dominant deep reddish color of the brick. As brick homes can be one of a myriad architectural styles, the only constant is the earthy red tone of brick and the effect you wish to create, whether the door blends in or "pops."
For a front door that blends seamlessly with the house facade, find a paint color that is highly similar to that of the brick. You might select a color of the same family, with a slightly darker or lighter shade. The monochromatic facade has the advantage of being a "safe" color scheme where you don't risk clashing colors. Look at variations in the coloring of individual bricks, and pick one that slightly stands out. Many paint suppliers can blend paint to match a small sample. Ask if they can match a chip of brick so that you can determine the precise color. As brick coloring can range widely, a monochromatic door may have a deep, berry hue or almost a terra cotta orange.
An adjacent color combination uses two colors that are located next to one another on the color wheel. For example, blue goes with the adjacent colors blue violet or blue green. In the case of a brick house facade, a reddish-orange brick could be paired with a deep red door. Brick that has a deep wine or burgundy color would combine well with a brighter, fire engine-red door. For adjacent color combinations to look best, you should combine colors with slightly different shades or intensities. If the brick is somewhat washed-out, use a rich and intense color for the door. If the brick is brand-new and saturated with color, a more muted tone may work well for the door.
For a complementary color scheme, two opposite colors are paired together. For example, red and green are located opposite one another on the color wheel, as are yellow and violet or blue and orange. Complementary color combinations are the riskiest and most delicate. It can help to select one dominant color and one subtler one, thereby avoiding an impression of "clashing" between the opposite colors. As most brick houses are somewhere between red and orange, complementary doors are either blue or green. Bright blue doors add a measure of cheer to otherwise staid brick exteriors. Kelly green or forest green both give a somewhat traditional, yet striking, contrast to brickwork.