It's easier to find stuff in a large tote if the lining is a light color. The lining also will play a role in the structure of the bag, depending on the outer fabric and the interfacing (or batting). The heavier weight the outside fabric, the lighter weight the lining can be because the outside fabric can handle the load. If you use a lighter weight outside fabric, like quilting cotton, you would want the lining to be at least as heavy, so make sure the muslin is a good quality. Also, use sturdy thread. I personally do not use cotton, I use a poly or poly cotton blend. I make lots of tote bags and I'm amazed at what folks put into them. If you are making it for someone else, assume that they are going to fill it with rocks (well, books). Double stitch seams and make sure the handles are attached really well.