Richard Scarry's Colors, a children's picture book by the eponymous author/illustrator, is free at B&N, courtesy of publisher Sterling.
This is a NOOK Kids Read to Me book and can only be read on the NOOKcolor, though non NOOKcolor owners can "purchase" if not download it for later use should B&N ever bring out an app.
Synopsis
With art by Richard Scarry, you know this is going to be more than your average color concept book: it educates and entertains too! Bright and fun to look at, it offers plenty of amusement and action on every page. And as they're enjoying the lively pictures, toddlers will learn some simple color basics in the most delightful way.
The other NOOKcolor freebie today is
The Elephant's Child, based on a Rudyard Kipling tale, and an older freebie,
The Twelve Hidden Days of Christmas, is apparently still free.
For more free B&N books, please see the excellent
Free NOOKbooks Summary Thread on their discussion forums, which prunes and updates the list every few days to keep it current.