Color theory is a complex study that centers on how colors relate to one another. Once you comprehend the concepts behind it, you will know why some colors harmonize well together, while others do not. I present only a sampling here, in order to to suggest how the theory might be used in landscape design.
For a deeper look into this important aspect of landscaping, please read my full article on color theory, which links to photos.
The spectrum is often divided into four color classes (I give examples of all four in my full article, cited above):
The spectrum of colors is represented as a wheel, divided into slices that stand for the various hues (colors). Using color theory, landscapers may refer to this wheel to choose adjacent colors in the spectrum, in order to provide unity; or they may deliberately juxtapose items directly across from each other on the wheel to make a contrast.
Thus you can achieve unity in your landscaping using color simply by grouping warm colors with warm colors (red, yellow and orange) and cool with cool (blue, purple and green).
In addition, proper application of color theory can influence the mood felt in a yard. For example, warm colors tend to excite the viewer, while cool colors are more likely to relax us. This makes a color like red a natural for focal points, and a color like blue a logical choice for meditation gardens.
Had enough with the theory for now? Consult my photo gallery of landscape color schemes for a more hands-on approach.