The six colors of the spectrum have contributed significantly to expressions and turns of phrase that are themselves often quite colorful. Here’s a sampling of idioms employing the words for colors.
Because of the association of the color red with danger and deficits, most idioms that include the word red — for example, “in the red” (meaning “in debt”) “red tape” (referring to bureaucratic complications), and “seeing red” (being so angry that one’s vision is blurred) — have negative associations.
However, they overshadow a few positive ones: “paint the town red” (enjoying oneself dining and drinking), “red-letter day” (an occasion for celebration), and “red-carpet treatment” or “roll out the red carpet” (referring to paying special attention to someone, based on the color of carpeting usually seen at the entrance to a gala event for celebrities or VIPs).
A red herring is a deliberate diversion, a red-eye flight is a late-night airplane trip (from the bloodshot eyes of tired passengers), and to have a red face or to go beet red is to be embarrassed.
Among the colors of the rainbow, orange is curiously absent from idiomatic usage. Although it is a bright, cheerful color often found in nature, the only common expression that uses the word orange employs the plural form referring to the fruit of that name –“apples and oranges,” meaning “unrelated subjects or issues,” to emphasize irrelevance.
The few idioms incorporating the word yellow have negative connotations. To have a yellow belly or a yellow streak down one’s back (the reason for the choice of locations is obscure) is to be a coward, and yellow journalism, based on an early comic strip character named the Yellow Kid, is that which is sensational and/or biased.
The phrases “green-eyed monster,” an epithet for jealousy, and “green with envy” are perhaps based on the idea that one’s complexion turns a sickly hue when feeling these emotions; similarly, to say that someone looks green (or is green around the gills) means that they appear to be sick.
But green also has positive connotations: To give someone the green light, based on the universal traffic-signal color to indicate “Go,” is to approve a proposal. If you have a green thumb (or, in British English, green fingers), you are adept in gardening — probably because successful gardeners are apparent from the green pigmentation that rubs off from healthy plants to their hands as they handle the vegetation.
Because US paper currency is green, in American English, the color is associated with money and wealth.
Because it is the color of the sky, blue is associated with idioms such as “out of the blue,” “like a bolt from the blue,” and “out of a clear blue sky” that refer to a person, thing, or idea that arrives as if from nowhere. (“Into the wild blue yonder,” meanwhile, refers to a venture into unknown territory.)
“Blue collar” connotes people who work at a trade or as laborers, because such workers at one time commonly wore durable shirts made of blue cotton (as opposed to “white collar,” referring to dress shirts worn by professionals and office workers, and “pink collar,” a later, now frowned-on, reference to women in clerical positions, so labeled because men rarely wore pink.)
Two idioms generally negative in sense include blue-blooded, meaning “aristocratic,” probably because during the era in which the term was coined, nobility tended not to spend time in the sun and their veins showed blue under their pale skin, and “blue-eyed boy,” referring to a favored protégé; this phrase likely stems from the fact that fair-skinned and fair-haired people, who at one time had a social advantage over their swarthier counterparts, are likely to have blue eyes.
Other negative idioms include the use of blue to refer to a sad or bleak mood, as well as “black and blue,” meaning “bruised,” from the color of bruised skin, and “blue in the face,” referring to someone trying (in vain) to persuade another until, from lack of breath, they attain this state.
Purple or Violet
Purple, also called violet, like its color-spectrum counterpart yellow, has little representation in idiomatic language: Purple prose is that which is overwrought or overly complicated, and a shrinking violet is a shy person, though the usage is usually employed in such phrases as “not a shrinking violet” to refer to someone who is anything but shy.
The color purple, because materials for dying fabric in that color were rare and therefore expensive, was reserved for royalty or the wealthy in western cultures and still has an association with nobility. This association resulted in another idiom, “born to the purple,” meaning “someone born to royalty during their reign” and, by extension, referring to children of prominent people.