My favorite book is
Colourwash Quilts by Deirdre Amsden, copyright 1994. I bought it shortly after it was published and still refer to it frequently.
Some other books are:
Watercolor Quilts, by Magaret and Slusser
Watercolor Impressions, by Magaret and Slusser
Impressionist Quilts, by Gai Perry
Watercolor Magic, by Deanna Spigola
Some eye candy from Google Images:
https://www.google.com/search?site=i...79.ty3rjlxhTMY
Try searching on Google, using "watercolor quilts", and "watercolour quilts", and "watercolor quilt patterns". As you search, there are further search suggestions at the bottom of the page.