Enliven a quiet spot with complementary colors opposite each other on the color wheel. In color theory, opposites are energy-packed visual experiences. Red is opposite green; blue is opposite orange; yellow is opposite purple. In the landscape, red and green are opposites, but the use of turquoise rather than true green bends the rules while still making a vivid statement. The horticultural equivalent might be a plant with lime foliage paired with a maroon or wine-color plant.