UNITED STATES—Flowers were originally colorful only to attract pollinators. Breeding has improved the color and quality of many garden varieties of flowers, to make them more appealing to the people who grow them. Some have been bred so extensively that they are sterile, which defeats the original function of flowers. Now their function is merely to look good in the garden. Improvements are relative.

Foliage is green because it is photosynthetic. Chlorophyll, which is necessary for photosynthesis, happens to be green. Yellow, red, blue, purple, bronze, gray and variegated foliage might not be as efficient at photosynthesis as green foliage, but can be appealing in home gardens. Many plants with colored foliage are inferior to their greener counterparts, but are somehow more popular.

Gray and blue foliage absorbs less sunlight, which can be an advantage in harsh environments. Blue hesper palm and the various blue agaves are from arid deserts. Colorado blue spruce is from high elevations of the Rocky Mountains. Arizona cypress, silver mountain gum, artemesia, lambs’ ears, lavenders, dusty millers and blue junipers all provide distinctively gray or blue foliage.

Golden arborvitaes and junipers can be strikingly gold as new foliage develops in spring, even if the color does not last long. Most plants with gold foliage fade to yellowish green through summer. Golden honeylocusts do not fade as much, so they are still mostly yellow by the time they defoliate in winter. Purplish or reddish foliage of purple leaf plum and red Japanese maple holds color better.

Euonymous, English holly, osmanthus, silverberry, hosta and various pittosporums can be variegated with white or yellow. Ivy, and hydrangea can be variegated with white. New Zealand flax and mirror plant can be variegated with gold or bronze, . . . or red or pink. Any unvariegated mutant growth (known as ‘sports’) that appears on variegated plants should be pruned away. Because it has more chlorophyl, it grows more vigorously, so can overwhelm and replace the more desirable variegated foliage.

Highlight: mirror plant

As the old fashioned larger mirror plant, Coprosma repens, fell out of favor through the 1990s, several more colorful varieties of a more compact species of mirror plant, Coprosma X kirkii, became popular. (The ‘X’ in the name indicates that it is actually a hybrid of two specie.) Without getting much more than two feet deep, it spreads out laterally like dense evergreen groundcover.

The color is not from bloom, but from the very glossy foliage. It can be variegated with white, gold, red, pink or bronze, or completely brownish bronze. Some varieties stay very shallow. Others can be shorn into low hedges like Japanese boxwood, only shorter. Although mirror plant does not mind partial shade, foliar density and color is best with full sun exposure and occasional watering.

Most modern varieties are known by their cultivar names, without their specie names. For example, Coprosma ‘Tequila Sunrise’ lacks the species name of ‘X kirkii’. Such omissions might be the result of confusing hybridization with Coprosma repens, for rounder leaves. In other words, some cultivars may be of ‘questionable parentage’. Some are just dwarf cultivars of coprosma repens.