It was a green with a yellow ribbon inside to mark its pages. On the cover was a picture of a girl in the forest under a toadstool.
Maybe Elsa Beskow wrote it?
Floris, a small publishing company based in Edinburgh, Scotland, publishes a lot of international picture books and nostalgic classics in translation; in addition to Swedish author Beskow, their list includes picture books by Astrid Lindgren (also Swedish) and Sybille von Olffers. Floris books are beautifully made, too: ours don't have ribbon markers, but they do have bookcloth bindings.
Bernheimer's The Lonely Book (published by Schwartz and Wade; an imprint I also like, but for different reasons) has a nostalgic feel of its own. It's about loving a library book and later, rediscovering it (at the library book sale, no less). I think we can all relate.