A week or so ago, I came across a copy of Dorothy and the Wizard in Oz that I added to my collection. The interesting aspect of this copy was the endpapers, an inventive design that was later adapted into the second cover design for The Emerald City of Oz.
This copy of the book is a first state in the primary binding, but with pale olive endpapers rather than the bright yellow usually seen in this book. The difference is shown in the photo, with the olive version above the standard yellow. I've run across this before, but associated the olive endpapers with copies bearing the secondary spine imprint - interesting to see them used in a primary binding!
A similar color change occurs in Snowbound, one of the poetry books illustrated by John R. Neill and also published by Reilly & Britton. The first state used yellow as a secondary color in the illustrations, while a later state has the same olive green seen here. Just another example of the many variants to be found!