Why are the Na'vi blue? James Cameron answered the question in a recent interview saying he wanted there be an "otherness" to the love story between Sully's avatar and the native alien, Neytiri. Since skin color is "such a big issue on our planet," Cameron decided to use that issue as a thematic driving point. Other skin tones were already taken by humans, while green was already a cliché in other alien movies. "We had big blue women, not little green men," Cameron said. No word on why the Na'vi's skin sparkles, but you have to admit it is a cool effect. In the film, the Na'vi still have red blood. So they still have high-oxygen carrying rates in their hemoglobin-filled blood cells. It's just a pigment in their tissue that makes them blue. Also, in an interview with Entertainment Weekly, Cameron mentioned another reason he chose blue, was that it is reminiscent of certain Hindu deities, which he likes conceptually.
Other interesting facts of about Na'vi and Avatar bodies are the noticeable differences. Avatars have smaller eyes and generally thinner lips than the Na'vi, and their necks aren't quite as long.
Na'vi have very large eyes and very full lips, and their necks are proportionately twice as long as humans. The Na'vi can also rotate their heads at an astonishing 180 degrees, like an owl can. Also, the Na'vi have a very distinct body shape. Aside from standing 10 feet tall, their bodies are long, and streamlined. They all have very narrow waists and hips (even the females), with broad shoulders and chests. The Na'vi have very high cheekbones and more rounded faces. Avatars tend to keep their human facial structure with slightly higher cheekbones. Also, the Avatars retain a small amount of facial hair - their eyebrows - whereas the Na'vi have none! One more very important difference that everyone should take not of is the number of digits the Avatars and the Na'vi have. The Na'vi have four fingers and toes, but eh Avatars, with their human DNA have five.... Another interesting fact; ever notice those sparkly markings on their faces, like bio luminescent freckles? Well, these markings are unique to each individual. No two are alike. Hmmm, I wonder if the Na'vi can have identical twins?