color-uncovered

coloruncovered is an informational, interactive app about how our eyes function (and play tricks on us) and how we perceive everyday images. I would say it would be best for middle school, up. There are some concepts that may not make sense for younger children. (You could, however, just select certain pages the younger ones would understand.)
Cost: Free
Pros: 100% interactive activities that make you want to know the reasons for the different scenarios. It doesn't just give all the answers, it makes you think why first. It has both movies to watch and explanations to read. Very creative. It makes you think differently about the way your eyes work. It also goes beyond our eyes and explains animals eyes and facts about technology.
Cons: Mentions of evolution and how we were underwater when our eyes went through different developmental stages.
Uses in education: This can be used in a science class when learning about the human body and how it functions. It could be part of a section on how eyes work/function. It can also be used in an art class for some "background" information on how we literally perceive art as well as a very short history lesson.