Red, orange, and yellow are warm colors. Blue, green, and violet are cool colors. The use of warm colors in the flower border of a small yard will give the illusion of little space. Conversely, the use of cool colors gives the impression of openness and space. In general, the smaller the area, the fewer warm colors should be used.
Good foliage is obviously vital in plants with short blooming periods.
Consider how much of the plant foliage will be usable and whether it is a positive or negative attribute. Ornamental grasses, and even handsome-foliaged vegetables like broccoli and asparagus can be used for effect. The most logical way to choose plants is first by location, second by period of bloom, then by height and width, and finally, by color. Location takes into account the amount of sun or shade and water required. This information is easy to find in books on perennials and in catalogs.