An orange (citrus sinesis), unlike many fruits, does not continue to ripen after being picked. An orange's skin color, however, is not necessarily an indication of its ripeness. An orange with a greenish skin may, in fact, be ripe. The skins of Florida oranges are commonly dyed "orange" to appear attractive to consumers.
The orange, a berry in the botanical (study of plants) classification of fruits, originated in southern China in about 2200 B.C. The Romans introduced it to Europe in the first century A.D. Christopher Columbus brought the orange tree to Hispaniola (the Caribbean island now consisting of Haiti and the Dominican Republic) in 1493. And in 1539, Spanish explorer Hernando de Soto planted orange seedlings in St. Augustine, Florida.
Orange cultivation was later undertaken in progressively westward locations across the United States. Attempts to cultivate oranges as far west as California, however, were initially unsuccessful. In 1873, two Brazilian navel orange trees from Brazil were planted in California. These orange trees, called the Washington navel, thrived and are considered the ancestors of all California navel oranges.
Sources: Brody, Jane E. Jane Brody's Good Food Book, p. 158; Panati, Charles. Panati's Browser's Book of Beginnings, pp. 103-4; Root, Waverly L. Food, p. 306.