Contrast leaf shape and color. I'm a sucker for almost any plant with gold, burgundy, or blue foliage. They look great with green and with each other. There are even sedges with brown foliage, like Carex buchananii . But even with green, you have a lot of choice.
Variegation is eye-catching.
The white edges of this Salvia nipponica 'Fuji Snow' stand out in this scene, even though it's the smallest plant in the arrangement. Variegated foliage, especially when rimmed in white, brightens my container combinations. Silver foliage is also an eye-opener, and Artemisia species and cultivars offer many choices. As with texture and form, go for contrast in colors, pairing bright and dark shades for best effect. Use a few flowers for accent Most container gardeners focus on flowers, but I use flowers only as occasional accents.