I think you are talking about the same kind of fabric. To me tonal and mottled are the same. They are both fabrics that "read" a certain colour but are not solid. Some quilters also call them tone on tone or quilter's blenders. They are the boring non descript fabrics that are essential in quilting to showcase your beautiful "wow" fabric. When I started quilting, these are the fabrics that I didn't know I needed. Now I have a bin of each colour and am always looking for more. At fabric sales, these are now the fabrics that I look for first and am especially happy it I can find some Moda Marbles. I can't help you with on line shopping as I have never done any.