Shameless pitch here - The Color Encyclopedia of Hostas or better yet, the New Encyclopedia of Hostas - both from Timber, both from Diana Grenfell and Mike Shadrack, are organized by color. They don't include the volume of plants that the Zillis book does, but they do include the hostas grouped by color order. That way, if you've lost a name, you can go to that color section and see if you can match it up. Also, the newest book (The New Encyclopedia) has a chapter on minis. And it doesn't cost $80.
Kathy Guest Shadrack