Unless plants are grown in isolation with a neutral gray background, there is also the effect of adjacent plants on our subjective look at their color. Colors next to each other on the color wheel relate harmoniously. Colors across from each other on the color wheel, such as red to green, blue to orange, purple to yellow, are called complementary colors. They have the strongest contrast. Just as a pinch of seasoning spices up a dish, too much can spoil it. A flower border designed mostly (I want to primarily, but that's a dangerous term here, liable to misinterpretation) with related colors, generally softened with some white to form tints of the chosen, more saturated colors, will gain some zing with just a soupcon of the color complement. Purple with violet, lavender, and lilac, and just a smidge of a pale yellow is attractive. A border entirely of equal amounts of true blue and saturated orange is harsh. Further, the adjacent color alters our perception of the color pair: just envision a square of turquoise against green. Very different from a square of turquoise against pink. Johannes Itten, The Elements of Color, is a lovely little book on this subject. Judy in overcast but still mild New Jersey