It's a lot easier to figure out which plants you'll choose and use if you know what color combinations work best together. While this page doesn't go into exact plant and flower combinations, it will be helpful as a guideline to follow for creating your planting ideas and schemes.
As far as landscaping and garden design goes, there are thousands of possibilities. There are countless secondary colors of different hues and tones that go completely off the color wheel. So we just use it to get a general idea and confirm or eliminate any ideas we may have.
Often you'll see planting combinations and design ideas that don't seem to fit on the color wheel. However, as you read these definitions, you'll see that there is an explaination as to why certain colors do work well with others.
Complimentary colors are those directly across from each other on the wheel.
The most common successful complimentary combinations you'll see in gardens are yellows and purples, Red and Green, Blue and Orange. They're called "complementary" because, when used together, they become very vibrant and have strong contrast with each other.
Complementary colors are useful when you want to make something stand out. For example, if you use a green background foliage and have red flowers as the foreground, the red will be extremely vibrant, visual, and appear to to be closer to you.
Colors at 90 degrees or at an "L" from the starting color also have a lot of contrast and so are also complimentary. For example, yellow - green, yellow - red, purple - green, purple - red.
Red and Orange, Blue and Green, etc. These are colors right next to each other on the color wheel. They usually match extremely well but don't create much contrast. Color combinations like these are good for very soothing feeling designs and where you want to create a comfortable calm atmosphere.
Analogous color schemes are often found in nature. And naturally they work harmoniously together and are pleasing to the eye. In garden planting ideas, this type of scheme often uses 3 colors to get good effect. Choose one color as the dominate display, a second one next to it on the color wheel as support, and a third color or a neutral (black, white, or silver/gray) as an accent.
The triadic color scheme uses three colors equally spaced around the color wheel. These type of combinations tend to be very vibrant.
To use a triadic planting scheme successfully, the colors should be carefully balanced. One main color should be chosen as dominate and use the other two colors as accents.
Split-Complementary color scheme
The split-complementary color scheme is a variation of the complementary color scheme. In addition to the chosen primary color, it uses the the two colors right next to its complement.
This color scheme has the same strong visual contrast as the complementary color scheme but is spread out more and appears softer. This is one of the easiest methods to use successfully and without much thought.
Double Complementary Color Scheme (Tetradic)
This scheme has a very wide range as it uses two sets of complimentary colors. To create a successful combination with this type of layout, you would need to choose one color as a dominant and then accent with the other three.
Monochromatic uses variations of a single color. A good example of this is a paint swatch card that has several different values of one color. This type of scheme is very simple and pleasing. You'll find this especially true within the green to blue range of the color wheel.