While blue is one of the most popular colors it is one of
the least appetizing. Blue food is rare in nature. Food
researchers say that when humans searched for food, they
learned to avoid toxic or spoiled objects, which were often
blue, black, or purple. When food dyed blue is served to
study subjects, they lose appetite.
Green, brown, and red are the most popular food colors. Red
is often used in restaurant decorating schemes because it
is an appetite stimulant.