A tremendous asset in every well-designed garden, white is a superb accent for brighter colors.  Further, as dusk approaches, no colors shine as brightly as white, glowing in an ethereal light.

 
There are many degrees of white, and it pays to consider the character of the white you are introducing into the garden.  Color combinations should either create harmony or contrast in the garden, and what experienced gardeners know is that white can fall into either category.  Inexperienced gardeners tend to ignore white when creating their first gardens, but white (and green) are keys to sensitive garden design.

Soft white or cream creates harmony within the garden, moderating the battle between strong colors; bright white creates contrast just as surely as orange next to yellow. 'Iceberg', a brilliantly white rose, will act as a nice buffer in the garden, but its presence will be as star, not supporting player. 'French Lace', a softer white, is a harmonizer, appropriate for softening the potential clash of competing colors.  

 
Gardeners have experimented with monochromatic gardens for centuries; the most famous of these types of gardens are 'white gardens', created by including plants with blooms of various shades of white.  White gardens are among the most simple, yet sophisticated and lovely, creations a gardener can imagine.

As an aside, white gardens often include pale yellow and/or blue flowers as complements to the overall scheme.

White gardens are not so simple to create, as one must meld flowers of often subtle tonal differences into a united whole.   Further, the success of any perennial garden depends upon the designer's ability to match the season of bloom of the inhabitants of the various plant groupings.   Thankfully, white roses can provide a season-long continuity as the various perennials each have their two to four week season in the sun.