Human and Animal Vision
Olympus Microscopy Resource Center- A very in depth article that explains how the human eye works, including color perception and colorblindness.
www.handprint.com- An excellent site about color theory, color vision, and color mixing or paints.
Exploratorium- A great tool that lets you mix colors together to learn about human color perception. As you adjust the color levels, imagine the effect of having a fourth primary color.
www.naturfotograf.com- A collection of UV images of natural objects, mainly flowers, which show many distinct features only visible in UV light. Also, lots of details about how to take your own UV pictures.
UV Reflection in Bird Plumage
University of Wisconsin- Article about two species of birds that distinguish each other using the UV reflection of their plumage.
Wikipedia- Introductory article on ultraviolet light.
NASA- Great background information about electromagnetic radiation, including visible and ultraviolet light.