A monochromatic motif is one which simply uses one colour. Though this may sound dull and dreary, it is amazing how many tonal and shade variations can be found within just one hue. This high-impact unicolour effect is terribly stylish and put together, and is likely the easiest theme to follow in regards to most hues, with the exception of white.
A word about white
The ever popular all-white garden treatments is, in essence, a monochromatic theme, but white itself being the absence of colour makes this style challenging. The fact is all whites lean slightly towards other tones. Creamy whites have hints of yellow and/or red; cooler whites have bits of blues or greens. Therefore, it is important to follow the all-warm or all-cool tone rule to avoid certain whites looking dirty by comparison.
White in the landscape also has the additional advantage of magical nighttime luminosity. Place white blooms, pots, or even garden sculptures to highlight steps and entry ways or along passageways to light the way for an evening stroll. This effect can also be greatly amplified by placing white poolside to take advantage of the reflective qualities of pool water and, more subtly, in plants with glossy foliage.
An analogous colour pallet is one where any two or three colours located next to each other on the colour wheel are used (e.g. red, red-orange and orange or blue, blue-violet and violet, etc.). In effect, the colours are similar and, therefore, blend together wonderfully in a soft and harmonious way. Just because analogous colours blend quietly does not mean they cannot be high-impact. Just look at how lovely Mother Nature’s take on this colour theme is showcased in the vivacious pinks and oranges of some Echinacea blooms.
Complementary colour motifs are bold and high-contrast. These colours are located opposite of each other on the colour wheel, such as violet and yellow, or blue and orange for example. Complementary motifs bring out the sheer joie de vivre of each colour involved. Just be conscious when selecting colours with a similar depth of vibrancy to avoid colour washout when placing them side-by-side. The complementary colour pairing is a classic, common-knowledge theme used across all aspects of art and design.