Blind people can 'see' things by using other parts of their bodies. This fact may help us to understand our feelings about color. If blind people can sense color differences, then perhaps we, too, are affected by color unconsciously (无意识地). (79) Manufacturers (生产商) have discovered by experience that sugar sells badly in green wrappings, that blue foods are considered unpleasant, and that cosmetics (化妆品) should never be packaged in brown. These discoveries have grown into a branch of color psychology. Color psychology now finds application in everything from fashion to decoration. Some of our preferences are clearly psychological. Dark blue is the color of the night sky and therefore associated with calm, while yellow is a day color with associations of energy and incentive (刺激). For a primitive man, activity during the day meant hunting and attacking, while he soon saw red as the color of blood and anger and the heat that came with effort. And green is associated with passive defense and self-protection. (80) Experiments have shown that colors, partly because of their psychological associations, also have a direct psychological effect. People exposed to bright red show an increase in breath, in heartbeat and in blood pressure red is exciting. Similar exposure to pure blue has exactly the opposite effect it is a calming color. Because of its exciting meaning, red is chosen as the signal for danger, but closer analysis shows that a vivid yellow can produce a more basic state of alarm. So fire engines and ambulances in some advanced communities are now rushing around in bright yellow colors that stop the traffic dead. Our preferences for certain colors are ______ according to the passage.