Where winters stay relatively warm, experiencing only a few light frosts, annual flowers can be used to liven the landscape.
The most common and perhaps hardiest winter annuals are violas and pansies. (These are actually the same plant, differentiated only by the size over the flower, with pansies being the larger of the two.)
Other possibilities include candytuft (Iberis umbellata), a low-growing mat with bunches of small white flowers; larkspur (Consolida spp.), with spikes or purple or blue bell-shaped flowers; sweet William and other pinks (Dianthus spp.), with small, frilly button-like flowers in all shades of pink and white. For a warm, sunny color, try pot marigolds (Calendula spp.).
For winter foliage interest, ornamental kale is a popular choice, but radicchio and colorful lettuces are becoming increasingly popular as ornamental edging.