I read this book about 10-13 years ago and since then I haven't been able to find the title and I would really like to read it again. This was in middle school (grades 6 - 8) so the book would have to address that age of audience.
From what I remember, the protagonist is a young boy. They live in a cave on boats. The boy is almost certain that they are simply going in circles since he has managed to swim around and get back to his home. At one point the boy manages to escape out into the world. He doesn't know what colors are, or what anything really is, but the main focus is on color (if I recall correctly). He meets a girl that explains to him what the things around him are.
That's all I can remember. Thanks in advance!