Mama Frog gets a big surprise when the guests arrive for Little Frog’s birthday party: Red Fox looks green to her! Orange Cat looks blue! With the active help of the reader, Little Frog shows Mama Frog how to see the animals in their more familiar colors. In this book, Eric Carle invites readers to discover complementary colors while enjoying the amusing story of Little Frog and his colorful friends.

“Once again proving the adage that less is more, Carle offers a straightforward, repetitive text and minimalist cut-paper art to demonstrate yet another dictum: Goethe’s 19th-century theory that there are three primary colors from which all others are made, and that each color has an opposite, complementary hue. In the simple story line, guests arrive at Little Frog’s birthday party and he greets them by name (e.g. Red Fox, Orange Cat, Yellow Bird). But Mama Fox and readers see these same pals as a green fox, a blue cat and a purple bird. By following Carle’s succinct introductory directions, youngsters can see things the way Little Frog does. After staring at each large-scale picture of an animal friend, then shifting their gazes to the blank page opposite, readers can see the creature’s faint, luminous image in its complementary color. Though it’s a concept that is, quite literally, mesmerizing, there are a few practical caveats: a reading location must be selected carefully, as the images are less visible in low- or brightly lit areas; some children (especially younger ones) may not have the patience to stare for the prescribed 10 seconds; and kids may be frustrated that the complementary color is pale and does not appear with the same intensity as the original. Still, Carle deserves praise for putting this rather abstract theory into practice in a tangible way. It’s very likely that readers and art lovers alike, if unsuccessful in their first attempts, will keep trying until practice makes perfect. Ages 2-up. ”
– Publishers Weekly, January 26, 1998

“Carle (From Head to Toe, 1997) asks readers to engage in optical illusions to view his illustrations for a story that becomes an unforgettable lesson in complementary colors.
By staring at a picture—e.g., the green fox on the cover—for ten seconds or longer, and then looking at a blank page, the picture reappears, in this case, the red fox of the title. The end papers feature helpful color circles so readers can locate colors and thus their complements. The story is minimal: As the animal guests arrive at Little Frog’s birthday party, they appear to Mama Frog to be the wrong color—for example, Yellow Bird is purple—until Little Frog teaches her the trick. Although it may take children time to master the gimmick (and the ghostly after-image, without the details of the original picture, may not meet their expectations), the ending neatly wraps this visual tale, with Mama Frog’s kiss transforming the green Little Frog to blushing red.”
– Kirkus Reviews, February 1, 1998