Originally published in 1994, this was one of the last books in the Serendipity series. This was set on Serendipity Island, which I think is the only land mass named Serendipity.
On this island, human-like creatures with golden-brown fur and a head looking like a cross between a lop-eared rabbit and a hound dog, live lives regimented by their favorite color. There's one guy who doesn't -- the Napoleon of the title. He's treated like a suspected pedophile.
Anyway, it doesn't take an English professor to figure out that the obsession for a particular color is a metaphor for obsession about races. The story is predictable, but enjoyable.
Serendipity is famous for the little rhymed morals at the end. Despite the plot and obvious metaphor, the moral just urged readers to try a change ... change just in general, alluding to nothing specific. It was much better than the usual heavy-handed morals.
Probably not the best idea to name a gentle, tolerant character after a ruthless tyrant, but it could be that Cosgrove wanted readers to be surprised that the character didn't act at all like his namesake.
The art wasn't as good this time around. Robin James was gifted in doing realistic animals, but for this series, she mainly had to do overly cute, huge eyed characters. Many of the illustrations have a slightly fuzzy look, as if it was a still from an older animated movie rather than a little painting.
You can currently find this book, and nearly all of the Serendipity series, at the Internet Archive.