There are many factors to consider when choosing plants for your garden. Once you've narrowed the list to plants that do well in your environment, it's common to start choosing plants by the color of their flowers or foliage. However, some garden designers argue that it's better to choose plants first by shape, then worry about color.
Imagine your garden as a black and white photo in each season. This will help you see its overall structure. Make a list of climate-appropriate evergreen and/or strongly architectural trees, shrubs and perennials that will ensure an interesting outline through the seasons. Then think about color to narrow the list.