Many of us are used to seeing those lovely bright orange oranges in the grocery stores. Here in Honduras and in other tropical areas, the oranges and lemons are usually green. In fact, by the time they start showing a little color, they are often past their prime.
Why is that?
Oranges are actually a sub-tropical tree that was introduced to the American tropics around 1500 by Christopher Columbus among others. The fruit does not continue to ripen after picking so it must be left on the tree until ripe. The natural orange color of Citrus sinensis (sweet orange) is brought on by cooler temperatures. Since most eating oranges in the US are grown in Florida or California, they receive a bit more cool weather than they get here in Honduras.
So if you are growing oranges in cooler climates, the peel will probably become orange, if you are growing them in the tropics, most varieties will stay green when ripe.
It's not only temperature, though. All sorts of dastardly things are done to make oranges orange for the consumer, including gassing them with ethylene gas, washing with detergent, coating with wax, and yes, even coloring them with dye.
Orange oranges can also turn green again, in a natural process called regreening. It can happen when oranges are left on the tree while the tree is blooming.
Whether it is orange or green, a ripe orange tastes the same.
Interesting tidbit: The English word 'orange' means both the citrus fruit and the color. The Spanish word 'naranja' also means both the fruit and the color, even though in much of the Spanish-speaking world, oranges are green.
For everything you ever wanted to know about oranges, see Fruits of Warm Climates, an excellent online book from Purdue University.