In 1975, George Carlin appeared on a popular TV show, Saturday Night Live, with his famous words about blue food. "Why is there no blue food? I can't find blue food--I can't find the flavor of blue! I mean yellow is lemon; orange is orange and red is cherry. Where is the blue food? " Well, Carlin pretty much has it right--there's not no blue food, but there's certainly not a lot of it. Fresh-picked blueberries are blue, though they become purple when they are turned into jam. The blue in blueberries--like the purple in grapes and the red in tomatoes--is found in nature. But it isn't a hot color for food. People don't seem to prefer blue food. Some diet programs even suggest that those determined to lose weight should make their food blue. Eating, in part, begins with our eyes. Charles Spence--an experimental psychologist from Oxford University--points out that color can change our taste experience. Commonly, we consider red-colored foods up to 20% sweeter than they actually are; and green foods as being more sour. Spence suggests: human expectations may be influenced by our long history of watching - green fruits can become sweet as they grow up and turn red. But what about blue? Except blueberries, much of the blue food we see these days _ blue artificially. Food producers argue that artificial color doesn't do much harm to health. A lot of research shows that some physical problems of kids are related to food dyes--while other studies show no effects at all. Blue birthday cake or even blue-dyed chicken can be served on the dinner table. So what? Eating sometimes begins with our eyes because   _  .
our taste experience can be influenced by color red-colored food are 20% sweeter than green food people prefer red-colored food to green food before eating, people watch food for a long time