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 color1. If they sense color1 differences, then perhaps we, too, are affected by color1 without knowing it.        Salesmen have discovered by experience over a long period of time that sugar sells badly in greenwrappings , 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 color1 psychology . Some of our preferences  for color1s are clearly psychological. Dark blue is the color1 of the night sky and therefore connected with calm, while yellow is a day color1 connected with energy and encouragement. Experiments have shown that color1s, 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 calming color1. Being exciting, red was chosen as the signal for danger, but a close study shows that a bright yellow can produce a more basic state of alarm, so fire engines in some advanced areas are now rushing around in bright yellow color1s that stop buses, trucks and cars. It can be inferred from the passage that   _  .
what color1 we prefer depends on our state of mind foods sell well in green or blue wrappings blind people cannot sense color1 difference a bright yellow has exactly the opposite effect to red