Monochromatic color schemes include different flowers that have various tints and shades of a single color such as a hummingbird garden that is primarily comprised of flowers with red tints and shades. Another popular monochromatic garden is an all-white garden sometimes called a moon garden since white is very vibrant in moonlight. Choosing a particular color can be especially effective in complementing the color of your house.
Analogous, complementary and polychromatic color schemes use several colors.
An analogous scheme uses two or more shades that are adjacent or neighboring on the color wheel. Yellow, yellow-orange and orange would be an analogous color scheme.
A complementary color scheme uses colors opposite each other on the color whee such as blue and orange.
A polychromatic scheme uses any and every color combination. Rich tapestry gardens are polychromatic. This type of design can be festive. It is important to mention that even these multi-colored gardens benefit from planned plant selection and placement.
Most references list flower colors. Don't forget foliage colors. A yellow edged hosta will be seen in a low-light garden before a blue hosta will. Silver foliaged plants can be used to blend areas. They highlight both warm and cool colors.
Earth laughs in flowers.
-- Ralph Waldo Emerson