Color Uncovered. Produced by the Exploratorium. Ipad. Free

Reviwed by Carl Zimmer

Late in his life, Claude Monet developed cataracts. As his lenses degraded, they blocked parts of the visible spectrum, and the colors he perceived grew muddy. Monet's cataracts left him struggling to paint; he complained to friends that he felt as if he saw everything in a fog. After years of failed treatments, he agreed at age 82 to have the lens of his left eye completely removed. Light could now stream through the opening unimpeded. Monet could now see familiar colors again. And he could also see colors he had never seen before. Monet began to see--and to paint--in ultraviolet.

We can turn light into vision thanks to the pigments in our eyes, which snatch photons and trigger electric signals that travel to our brains. We have three types of pigments tuned to violet, green, and red light. Birds, bees, and many other animals have additional pigments tuned to ultraviolet light. Ultraviolet vision has led to the evolution of ultraviolet color patterns. In some butterfly species, for example, the males and females look identical to the ordinary human eye. In UV light, however, the males sport bright patterns on their wings to attract the females. Many flowers have ultraviolet colors, often using them to get the attention of pollinating bees.

While each kind of pigment responds most strongly to a particular color, it can also respond more weakly to neighboring parts of the spectrum. The violet-tuned pigment, for example,can respond wealy to ultraviolet light, which has a higher frequency. Most of us don't get to experience that response, because our lenses filter out UV rays.

But Monet did. With his lens removed, Monet continued to paint. Flowers remained one of his favorite subjects. Only now the flowers were different. When most people look at water lily flowers, they appear white. After his cataract surgery, Monet's blue-tuned pigments could grab some of the UV light bouncing off of the petals. He started to paint the flowers a whitish-blue.

I just learned about Monet's super-vision while reading the lovely Color Uncovered, produced recently for the iPad by the Exploratorium of San Francisco, one of the best science museums on Earth. I don't quite know what to call Color Uncovered. Its iTunes page describes it as "an interactive book that features fascinating illusions, articles, and videos." Yet it feels like an elegantly designed museum exhibit poured into an iPad. Making matters more confusing, you have to go to the education category of the app store in iTunes to find it. When it comes to describing what it is we review here at Download the Universe, words often fail us. Sometimes that's a bad thing, because we're reviewing muddled products of muddled minds. In other cases--like this one--it just means that someone is making good use of several different genres, and melding them into something for which there's no good label.