News Home & Design Illustrator's Dazzling Work Highlights the Magic of Blue, Nature's Rarest Color 'The Blue Hour' celebrates this precious color, and the twilight time when blue is most apparent. By Kimberley Mok Kimberley Mok Twitter Writer McGill University Cornell University Kimberley Mok is a former architect who has been covering architecture and the arts for Treehugger since 2007. Learn about our editorial process Updated March 22, 2021 01:51PM EDT Fact checked by Haley Mast Fact checked by Haley Mast LinkedIn Harvard University Extension School Haley Mast is a freelance writer, fact-checker, and small organic farmer in the Columbia River Gorge. She enjoys gardening, reporting on environmental topics, and spending her time outside snowboarding or foraging. Topics of expertise and interest include agriculture, conservation, ecology, and climate science. Learn about our fact checking process Share Twitter Pinterest Email Éditions courtes et longues, 2015 News Environment Business & Policy Science Animals Home & Design Current Events Treehugger Voices News Archive Nature is a treasure trove of incredible colors. From the burnt sienna tones of a late autumnal landscape, to the dusky purple and heavenly rose of a sky that's just about to tip over into the evening hours, nature is always putting on a feast of color and profound pageantry for us to appreciate. But despite having so many colors at its disposal, scientists agree that there is one color that is the rarest of all: blue. That relative rarity is what prompted Paris, France-based illustrator and author Isabelle Simler to create these delightful images of various animals and insects, decked out in this most unusual of colors. Éditions courtes et longues, 2015 Gathered in a book aptly titled "The Blue Hour," Simler's vibrantly cross-hatched representations of blue-tinted organisms takes us on a visual journey through the natural world, pointing out all the diverse instances of these gorgeous blue hues: from a solitary bluejay with wings of almost iridescent rainbowed streaks, perched on a pale blue branch – to blue-toned foxes, poison dart frogs, Russian Blue cats, to the dark navy depths of an endless ocean. Éditions courtes et longues, 2015 Not only is the book a homage to a certain color and its variants (the book jacket lists no less than 32 different blue hues), it's also celebrating a certain time, as Simler's sparse but precise text reads: "The day ends.The night falls.And in between…there is the blue hour." Éditions courtes et longues, 2015 Fascinatingly, the blue hour is an actual period during the day which occurs when the sun is positioned well below the horizon, and the indirect sunlight that remains takes on a recognizably blue tone. Éditions courtes et longues, 2015 The blue hour is a part of a fluid and ever-ephemeral spectrum of possibilities in nature, which is beautifully highlighted by Simler's words: "[T]his time of day, when daytime animals enjoy the last moments before nighttime animals wake up. This in-between where the sounds and smells are denser and where the bluish light gives depth to the landscapes." Éditions courtes et longues, 2015 Simler's eye for detail arises from her careful habit of looking at things closely before even putting tools to paper. As she says in this recent interview about another one of her captivating children's books, "A Web": "The first step is observation. I am researching a lot upstream. Still images, but also moving images, to understand the movement of the body, legs... I like this stage of discovery that inspires me a lot. The first drawings, sketches and structure of the book are often done with colored pencils. The next step, the big spreads of the book are drawn directly on a graphics tablet connected to my computer. I like this tool which is very precise and allows me to enter the details of my drawings with a lot of finesse. So far I have always used this tool for my picture books. The drawing is transformed over time. It is not frozen and that's what makes the adventure interesting." Éditions courtes et longues, 2015 Simler's observational approach is what makes "The Blue Hour" so refreshing: it offers children (and their parents alike) a stylized look into the fascinating scientific fact as to why blue is so rare in the natural world. Even most animals that appear blue don't actually produce the pigment themselves, as Catie Leary once explained in "10 Elusively Blue Animals": "While plants can produce blue pigments thanks to anthocyanins, most creatures in the animal kingdom are unable to make blue pigments. Any instances of blue coloration you come across in animals are typically the result of structural effects, such as iridescence and selective reflection. Take, for example, the bluejay. This little bird produces melanin, meaning it should technically appear almost black. However, tiny air sacs in the bird's feathers scatter light, making it appear blue to our eyes. This is called Rayleigh scattering, a phenomenon that is also responsible for the age-old ' why is the sky blue?' question." Éditions courtes et longues, 2015 It's a match made in heaven: books like Simler's "The Blue Hour" marry the importance of exploring such scientific questions with deeper artistic contemplations, creating a work that will no doubt spur readers to find out more about the natural world around them. To see more, visit Isabelle Simler and her Instagram, and you can purchase "The Blue Hour" here.