The most common type of mold that grows oranges and other citrus fruits is called penicillium digitatum. It is very aggressive and causes post-harvest fruit decay.
Another type of mold that affects oranges is known as penicillium italicum and is the type of mold that is blue-green in color. Penicillium digitatum is olive-green in color; however, both species of mold contribute to a condition known as blue mold rot or storage rot. While certain foods, including some hard cheeses, can be safely consumed after the mold has been trimmed off, oranges should be discarded when affected by mold as they may cause sickness.