Those are translucents. So when you take a picture the skin appears that color because there isn't any pigment. The skin doesn't reflect light, it more like absorbs it when you take a picture.
Here is how the article on exotic forums explains it:
Translucent
These animals are well recognizable by their genetic disorder; they carry large pieces of translucent (transparent) skin. It's most extreme in young animals, with aging the skin will thicken. However, the translucent appearance remains. The genetic disorder implies the lack of white pigments. The iridophores* and leucophores** are missing, they lack white pigment. Light is able to pass through, giving a clear translucent effect.