People instinctively prefer to eat fruits and vegetables with bright colors, because vibrant coloring is a sign that the food contains healthy nutrients. Growers sometimes capitalize on our instinct to select colorful food by enhancing the color of fruits and vegetables with dyes that are approved by the U.S. Food and Drug Administration.
Food companies sometimes spray red dye on red delicious apples, fresh strawberries and red potatoes to enhance their appearance. Red dye is also used to color Maraschino cherries, which are often found in ice cream parlors for toppings, and in bars for making drinks. The FDA allows companies to add red dye to naturally red sweet potatoes to enhance their color, and also permits companies to dip oranges in red dye to make them look more orange.
Green products, such as pickles, sometimes have yellow dye to enhance their green color. The FDA allows oatmeal manufacturers to use yellow dye to color bits of apples to make them look like peaches in instant peach-flavored oatmeal. Food companies also add yellow dye to enhance the appearance of processed potatoes au gratin.
There aren't a lot of blue foods, but the FDA permits food processors to spray blue dye on blueberries, as well as on fruits that have some blue in them, such as strawberries, cherries and red delicious apples. Guacamole dip sometimes has blue and yellow dye added to it to make the avocado look greener.