Food coloring
Most people are aware that food with bright or unnatural colors, such as the green ketchup mentioned, contains food coloring. Far fewer people know that "natural" foods such as oranges and salmon may also be dyed to hide natural variations in color. The color of foods varies through the seasons. Processing food and storing it may change its color. For these reasons, it may give a commercial advantage to add colors to food, so that it has the color expected or preferred by the customers. Some of the main reasons are: