This is the second in a series about how to create a garden that is a unified work of art. When thinking about how to use color to unify your garden, the first color to think about is green. Green is the color of of the plant pigment chlorophyll, so most leaves are in shades of green. A garden that is just shades of green will feel very unified, and there are so many shades of green that it will have quite a bit of variety, a green garden can contain shades from the palest green to almost black. Some shades of green are almost yellow, others are almost blue.
Gray foliage can also unify a garden.
Most gardens have some green in them, and all gray gardens tend to be a bit dull without flowers to enliven them, so gray foliage is probably best used as a theme to weave throughout the garden. The advantage of gray foliage over green is that while some shades of green clash a bit with each other, shades of gray always harmonize with each other and gray goes with every flower color. Colored foliage is more often used for contrast than for harmony. It is possible to have a garden dominated by red or golden foliage, but such gardens are usually features within a larger garden. A way to integrate such a feature into a larger garden is to use plants with colored foliage in positions where you might place a piece of sculpture.