Complementary colors, when used together in color schemes, are especially dynamic and pleasing to the eye. This is because different types of cones (the photoreceptor cells in your eye that contribute to color vision) perceive different colors of light. If you stare for a long time at a block of color and then quickly look at a white wall, you'll see a light afterimage in the opposite, or complementary, color.
For example, let's say you're staring at a blue square. (You can try this out at the bottom of the page here.) After a while, the cells in your eye that process blue light will become fatigued, making the signal they send to your brain slightly weaker. Since that part of the visual spectrum is slightly suppressed, when you look at a white wall after staring at the blue square, you'll see a faint orange afterimage. What you're seeing is the white spectrum of light from the wall, minus a tiny bit of blue, which your brain processes as orange.
So what does this mean for the decorator? It means that combinations of complementary colors are especially dynamic together, since they play up each other's intensity. A tiny bit of orange really pops in a blue room (and vice versa) because your eye wants to see that color. A combination of two complimentary colors may be perceived as soothing or balanced, since it simultaneously stimulates different parts of the eye. Don't believe me? Check out some of the examples below.
Orange and Blue
This is my favorite of the complementary color matchups. Cool blue and punchy orange are such an odd couple, yet when they come together they make such beautiful music. I love how in the photo above (from House Beautiful via Cottage Modern), the orange in the blanket really seems to jump right off of the page.
Yellow and Purple
In this interior from Tilton Fenwick, an ombre painting in delicious tension with those distinctive yellow spines. Look at the yellow candle below the painting. Is that not the yellowest yellow you've ever seen? Science at work.
Red and Green
Naturally, it's hard to see these colors together without thinking, "Christmas!". The secret to this, I think, is to pull one of the colors away from the traditional Yuletide emerald green and bright crimson red. The example above (from Mires Paris via Lamps Plus) works because the ceiling leans a little towards magenta. Of course, in the Indian bedroom below, the colors couldn't be more Christmas-y, but somehow it works — proof that rules are made to be broken.
What do you think? Feeling inspired to try out one of these bold combos?
(Images: as linked above)