Passage Three

Questions 31 to 35 are based on the following passage.

Human feelings are affected by colour unconsciously. Manufacturers have discovered by trial and error that sugar sells badly in green wrappings，that blue foods are considered by consumers as tasteless，and that cosmetics should never be packaged in brown. These discoveries have grown into a whole discipline of colour psychology. Some of our preferences are clearly psychological. Dark blue is the colour of the night sky and therefore associated with quiet and calm：White yellow is a key colour in association with energy. For primitive men，activity during the day time meant hunting and attacking，which he soon saw red，the colour of blood and the fire. So it was natural that green, the complementary colour to red，should be associated with passive defence. Experiments have shown that colours also have a direct psychological effect. People when exposed to bright red，show an increase in breathing rate，heart beat and blood pressure. Red is exciting. Similar exposure to pure blue has exactly the opposite effect，because it is a calming colour. Because red has an implication of exciting，it was chosen as the signal for danger. Some analysis shows that a vivid yellow can produce a more basic state of alarm. So fire engines and ambulances in some advanced countries are now rushing around in bright yellow colours that stop traffic deed.

 The passage is about______.