Complementary colors provide eye-catching, dramatic plantings. Complementary colors are opposite each other on the color wheel. These might include planting blues with oranges, purples with yellows, or reds with greens. Some of my favorite designs include complementary plantings. Purple nierembergia is wonderful planted with the deep yellow Dahlberg daisies.
Harmonious colors are next to each other on the color wheel.
Examples would be combinations of red with purple or orange, blue with purple or green, yellow with green or orange, or orange with yellow or red. These plantings are not as vivid but have a more softening effect. This is why red geraniums look at home surrounded by violet and pink lobelia or alyssum. Monochromatic plantings can also be quite attractive. These color schemes use different flowers in a single color throughout a flower bed.