Color theory refers to the aesthetic art of mixing colors and the visual effects of those color combinations — to create a relaxing feel, make small spaces seem larger, attract attention to an area or tie areas together, for example. In landscaping, the color spectrum is divided into four groups:
Primary: reds, yellows and blues
Secondary: greens, violets and oranges
Tertiary: blends of primary and secondary colors
Neutral: white, gray, tan and silvers
Using color combinations, you match colors to complement each other and tertiary colors are often used as transitional colors.