Red
Red, a color. Orange-red is a primary color of light. When mixed with violet-blue and green light, it forms white light. Magenta, a reddish purple, is a primary color of pigments. Black is formed when magenta, cyan (a greenish blue), and yellow pigments are mixed. Red has the longest wavelength of all colors.
Red is the color of blood in mammals, birds, and fishes. It is commonly used to signify danger, and is used to indicate "stop" in traffic and railway signals.
Red is a warm, stimulating color. Red objects seem to be nearer than they actually are and for this reason artists call red an advancing color.
Red symbolizes varied things, including love, life, passion, courage, anger, heat, fire, and war. A red flag is symbolic of revolution. Red roses signify love. Some common phrases in which red has a symbolic meaning include the following:
A red-letter day is a memorable one. The expression comes from the practice of marking festivals in red on church calendars.
To be in the red is to be in debt or to be losing money, because bookkeepers formerly showed debts in red ink.
To be caught red-handed is to be discovered in the commission of an offense, as a murderer would be if surprised with the blood of his victim on his hands.
To see red is to be furious. The term comes from the erroneous belief that red infuriates bulls. (Bulls see only in black and white.)
A red herring is a subject introduced to turn attention away from the main question. The term comes from the belief that a bloodhound can be decoyed from a trail if a red herring (a type of smoked herring) is drawn across it.