According the passage, we may know that salesmen have______.

The fact that blind people can see things using other parts of their bodies apart from their eyes may help us understand our feeling about color. If they sense color differences, then perhaps we, too, are affected by color without knowing it.
    Salesmen have discovered by experience over a long period of time that sugar sells badly in green wrappings, that blue foods are considered not agreeable to the taste, and that cosmetics should never be packed in brown. Their discoveries have grown into a whole subject of color psychology. Some of our preferences for colors are clearly psychological. Dark is the color of the night sky and therefore connected with coward, while yellow is a day color connected with energy and encouragement. Experiments have shown that colors, partly because they are connected with psychology, also have a direct effect on people’s mind. People in bright red surroundings show an increase in breathing speed, heartbeat and blood pressure; red is exciting. Pure blue has exactly the opposite effect; it is a relaxing color. Being exciting, red was chosen as the signal for danger, but a close study shows that a bright yellow can produce better effect of alarm, so fire engines in some advanced areas are now rushing around in bright yellow colors that stop buses, trucks and cars.