Coloration can arise either directly through the presence of visible colored cells such as those in freckles, or indirectly by virtue of cells such as hair follicles imparting pigments to the non-living elements such as fur, feathers and scales that grow from them. In many cases such elements are arranged in a highly regular way, often in a repetitive hexagonal pattern. Evolutionary optimization is often used to explain observed pigmentation patterns—with varying degrees of success. The notion that for example the stripes of a zebra are for camouflage may at first seem implausible, but there is some evidence that dramatic stripes do make it harder for a predator to recognize the overall shape of the zebra. Many of the pigments used by animals are by-products of metabolism, suggesting that at least at first pigmentation patterns were probably often incidental to the operation of the animal.