Colorful food in nature = antioxidants = more nutrition.

Why is this?
Most of the nutrients in a fruit or a vegetable can be found in the pigments - the substance that give foods their uniqe color. So the deeper the color is, the higher the levels of antioxidants it contains.
This is why you should never peel your apples or other fruits. If you're peeling the fruit because you don't want to ingest pesticide - then buy organic fruit which are pesticide-free instead.

While blueberries will always be blue, tomatoes can be either red, orange or yellow. Choose to eat the red ones as these contains more of one of nature's most powerful antioxidants - lycopene. This antioxidant helps preventing prostate cancer, among things.
Same "rule" goes for apples... Choose the red ones over the green and yellow ones.