The fact that blind people can "see" things using other parts of their bodies apart from their eyes may help us to understand our feelings about colour. If they can sense colour differences then perhaps we, too, are affected by colour unconsciously.
Manufacturers have discovered by trial and error that sugar sells badly in green wrappings, and that blue foods are considered unpleasant, and the cosmetics should never be packaged in brown. These discoveries have grown into a whole discipline of color psychology that now finds application in everything from fashion to interior decoration. Some of our preferences are clearly psychological Dark blue is the colour of the night sky and therefore associated with passivity and calm, while yellow is a day colour with associations of energy and incentive. For primitive man, activity during the day meant hunting and attacking, while he soon saw as red, the colour of blood and rage and the heat that came with effort. And green is associated with passive defence and self - preservation. Experiments have shown that colours, partly because of their psychological association, also have a direct psychological effect. People exposed to bright red show an increase in heartbeat, and blood pressure; red is exciting. Similar exposure to pure blue has exactly the opposite effect; it is a calming colour. Because of its exciting connotations (涵义) , red was chosen as the signal for danger, but closer analysis shows that a vivid yellow can produce a more basic state of alertness and alarm, so fire engines and ambulances in some advanced communities are now rushing around in bright yellow colours that stop the traffic dead.
Manufacturers found out that colour affects sales（）。
A. by experimenting with different colours
B. by experience over a long period of time
C. by trying out colour on blind people
D. by developing the discipline of colour psychology