Red is the colour of blood, and this can mean health, as in a ruddy complexion or red cheeks, or it can mean violence, as in red with blood.
Red is the colour of passion, energy and motivation. The hue of fire as well as blood, it is associated with the Root Chakra, where we hold our deep unconscious beliefs about the basic safety of the world.
Red is also the colour of embarrassment; we blush red. In like manner, it indicates anger, as when we "see red." The simile "like a red flag before a bull" reflects the same idea.
Red-blooded people (a term usually applied to males) are full of vigour, virility and high spirits. Red also expresses love and passion. Red roses symbolize love and the ruby is one of the four precious gems, its hardness second only to that of the diamond.
Red-green colour blindness describes a visual condition that makes it impossible to distinguish red from green. Red is one of the colours of autumn leaves.
Red means danger. Both literally and metaphorically, a red light means stop. And red also symbolizes communism, leftism, socialism. Paradoxically, a redneck is a conservative, often bucolic type who occupies the opposite side of the political spectrum.
In China, red is the colour of happiness, widely used in New Year decorations and wedding clothes.
Lots of red foods are healthy: think tomatoes, beets, strawberries, and watermelon. But wait -- beets are really purple, aren't they? Maybe, but that doesn't stop us from turning beet red.