http://www.kathkwilts.com/lessons/watercolor.html
http://www.hgtv.com/hgtv/cr_quilting_other/article/0,1789,HGTV_3305_1371577,00.html
You might want to Google "colorwash quilting" or "watercolor quilting" to find more. Most of what I found by doing that was advertisements for books, kits and workshops