When planning a new planting scheme you need to be aware that the colors you choose will affect the mood of the garden. Color combinations can can provide a vibrant feeling or a calmer tone depending on your choice of plants. I came across an article by Martha Smith, a University of Illinois Extension horticulturist which has some helpful tips on how to make the best use of color.

When used effectively color can create a feeling of excitement or a sense of peaceful calm in the garden, said Martha Smith, a U of I Extension horticulturist.
“Colors can make a large space more intimate yet make a small space feel larger” said Smith. “Simply understanding the importance of color and how to use it can change the overall look and mood of your garden.
“Color is a personal matter. People are always looking for rules to follow. Really, we can only offer guidelines and they can be bent to satisfy personal taste.”
When planning a garden, think of it as a three-dimensional painting, and the plant colors as colors on an artist’s palette. Some colors will dominate and be spread with broad-brush strokes, while other colors will give depth and dimension with small dabs. Try to envision the entire garden…how you want it to look.

Have a color plan. Do you envision a monochromatic color scheme where all the flowers share the same pigment? An example would be red, pink, and burgundy impatiens planted among pink and red astilbe. Or perhaps you see a polychromatic scheme…. a rich tapestry of many colors. A color wheel is very handy. A complementary scheme uses colors that are directly opposite each other on the wheel. Examples are red and green, orange and blue, yellow and violet. Some very striking combinations can be made with complements.

See more at the U of I Extension