One of the best ways to make your garden visually interesting is to aim for contrast between your plants. This includes contrast in shape and texture, but also, and perhaps most importantly, in color. Flowers eventually fade, but plants with interesting foliage color can last through the entire growing season, or even all year as in the case of evergreens. However, foliage coloring alone doesn’t get the job done, you need to contrast plants together to really make them pop. Yellowish-green next to yellowish-green just looks like yellowish green. Put a yellowish-green plant next to a reddish-green plant though and the contrast makes both colors pop and look like brilliant yellow and vibrant red.
Source: Backyard Gardening