Decisive factors in the way colour affects us are light oscillations, our experiences, associations, and the symbolism learnt in our own culture.
Yellow is the colour of the sun, of light: it radiates happiness and optimism, but is also a warning colour for poisonous, explosive, or radioactive substances and in traffic lights. Yellow is intellectually stimulating.
Red is the colour of blood, fire, and war—but also represents love and passion. Red stimulates our mood.
Blue is the sea, sky, and infinity. It is the colour of the gods and a symbol of purity and beauty. Blue has a calming effect on us.
Green is nature, spring, hope, and contentedness. Green symbolises fertility and growth—and sometimes immaturity too. A green environment is calming, regenerating, and assists concentration.