Unfortunately, it took a little more time thank three years. But the stamp is now a reality in 2017!
The press release from the United States Postal Service goes on to say:
Each of the four new stamps in this 20-stamp booklet features a different illustration of main character Peter exploring and playing in his neighborhood while wearing his iconic red snowsuit. The images include: Peter forming a snowball, Peter sliding down a mountain of snow, Peter making a snow angel and Peter leaving footprints in the snow.
Since the publication of this treasured tale five decades ago young readers have enjoyed joining Peter on his winter adventure. Unlike most popular children’s authors at the time, Keats made a point to feature ethnically and racially diverse characters in his work. Inspired by a series of 1940 Life magazine photographs of a young African-American boy, Keats began writing The Snowy Day. Using paper collage, fabric, stamps and India ink, he crafted the unique look of the story’s wintry urban landscape.
Edited by Annis Duff and published in 1962, The Snowy Day has become a classic. Since its release, it has sold millions of copies.
As Peter starred in six more Keats stories, readers watched him grow older in print. Before the author’s death in 1983, he wrote and illustrated 22 children’s books and provided artwork for dozens more. Countless readers identified with his characters and stories, which brought added diversity to mainstream children's literature.
https://about.usps.com/news/national-releases/2017/pr17_058.htm