The answer to this classic question really depends on your point of view. Does the American flag have white stripes on a red background or red stripes on a white background? Is it a vase or two faces? Why can't it be both?

Despite tremendous diversity in patterns (a zebra's stripes are as distinctive as a human's fingerprints), there is no such thing as a solid black zebra or a solid white zebra that we can view as a "base model." (Albino zebras are lighter, but still striped.) All of them have both black stripes and white stripes — you can't have one without the other — and neither colour is obviously the "background."

If forced to take a stand, I'd say that a zebra is black with white stripes. Here's why:

1. You may have noticed that some zebras have white, unstriped underbellies and rumps. And where the striping is least dense, white becomes the prominent colour. This would seem to be strong evidence that the zebra's coat consists of a white background with black stripes "painted" over it. However, the colour of the hair does not indicate the base colour of the animal. The white belly could be just as much of an "addition" as the white stripes. And, in fact, a zebra's skin is black.

2. When zebras are crossbred with horses — creating zorses! — the offspring are often brown with darker-brown stripes, suggesting that the black stripes are the genetically transferable element. But this could just as easily indicate that the zebra pattern comes from the white stripes — white stripes blending with a dark base could create light-brown stripes interspersed with dark-brown stripes from the background. So this is inconclusive.

3. There are three extant species of zebra, all with black-and-white stripe patterns. A fourth, now extinct, species called the quagga had zebra striping in front, fading into a solid brown rump. This suggests that the evolutionary ancestor of the zebra may have had a solid, dark colour, to which white stripes were "added" as an evolutionary trait. The quagga could represent an intermediate species that didn't go "full monty" with the striping.

4. Along those evolutionary lines, if the zebra's ancestor did indeed start out as a solid colour, evolving stripes later, it seems much more likely that it started out dark, rather than white. It's highly unlikely that a solid white species of mammal could survive long on the African savannah.

5. The pigment of the zebra's coat is found only in the hair, not in the skin (which, as previously noted, is black). The black colour comes from pigment activation while the white colour comes from pigment inhibition. This means that the hair is naturally black, except when the pigmentation is "turned off."

Sources: HowStuffWorks, MadSci Network, ZebraMania, The Ultimate Horse Site