As a little girl, I wasn't on the bandwagon of having a favorite color. By now, I have changed my tune. Fruits and vegetables in purple are the best color of all, and this post explains why.
My bias in food is always based on health and flavor. Fruits and vegetables violet in color are especially "nutrient dense" (nerd speak, meaning lots of vitamins and things good for you). Also, they taste good, so I eat them whenever possible.
The healthy parts are in the anthocyanins (greek for blue flower) and betains. Both are purplish pigmented antioxidants, which benefit your heart. There are about 300 known anthocyanins and about 50 known betains. (I said about, as various antioxidants and their nutritive potential is an exploding field of nutrition research right now. There is still a lot to be uncovered.)
Purple containing plants contain more antioxidants than what you can see. When torn, purple leaves are often green on the inside, and the green you see is from chlorophyll. Try doing this with a piece of purple thai basil. The violet is actually created by the plant to protect itself and to protect the chlorophyll. This explains why (green) chlorophyll is located inside of the leaf, and why (purple) anthocyanins are on the outside. In fact, all antioxidants (of which there are thousands) are created to protect the plant itself from oxidants, like the sun and passing of time. Then, you eat those antioxidants and you are protected from the sun and time. This fact is a great sell on why we should consume plant foods at every meal. Also, I'd be willing to bet there are betacarotenoids (antioxidants orange in color) hiding in purple fruits and veg, but we would have to get into a laboratory to find out. Maybe the beans pictured below could be used in the experiment.
We are accustomed to seeing green broccoli, white cauliflower and red tomatoes, but most items we're used to seeing in one color comes in other hues too.
Modern farming practices have led us to whittle down the diverse quantity of plant foods to get one standard type, like a red apple. Don't let them fool you - there are about 5,000 varietals of apples.
Cooking Purple fruit and veg are beautiful in their raw state, but know there will be visual changes from cooking. Anthocyanins and betains are water soluble, and boiling will cause color to bleed out. Acid and base also have an effect. If you take purple cabbage and add an acid like lime juice, it will become more red in color (delicious tip --> Iime + purple cabbage is a great start to an asian slaw recipe). When a base is added - like tap water - the cabbage becomes more blue in color. (These blue and red changes are both result of transferring -OH groups, by the way).
There you have it- purple plants contain anthocyanins, betains and a whole lot of pretty. We eat first with our eyes and second with our heart --> so enjoy yourself and take care of that heart!