I recently finished Shades of Grey, one of the most enjoyable novels I've read in a while. When someone at work asked me what it was about and I responded with "It's a world where people are separated into classes by, er, color," I quickly had to revise my summary as he said, "Oh, that sounds familiar."
So there is an unavoidable social commentary aspect to this novel about a world where people are separated into classes by the color they can see. In this alternate future (maybe) Britain (maybe), everyone is selectively colorblind. Your social standing is determined by what colors you can perceive. The world grabbed me to the extent that I had a dream about gleefully telling someone I could see purple neon lines in the floor.
Because it's Jasper Fforde (who wrote the Thursday Next novels (which everyone should read), the alternate world is absolutely complete. Someone in the blurbs said that the more knowledgable you were the funnier it got, and it's true; if you read it, try Googling some of the terminology. Because it's by Jasper Fforde it is also occasionally hilarious. One particularly tense and frightening scene is interrupted, except not really at all because the moment passes so quickly and is so dryly stated, with the word pwoing.
One thing I couldn't help realizing is that another author used a similar concept years ago. I read The Seventh Tower back in grade school. Its protagonist is an Orange instead of a Red like Shades of Grey's protagonist. Being written for kids, The Seventh Tower contained a less complex world, fewer puns, and more monsters. It was also, amusingly enough, published by LucasBooks. But it stuck in my head long enough that it's still on my mind (and my shelf) today.
I never finished the Seventh Tower series. I am, though, going to be on the lookout for the rest of the Shades of Grey trilogy.