Any muslin would work if it's 100% cotton or just use a good solid cotton fabric, preferably white. Do not use the blends. If you use light colors like tan or beige or light yellow, that will affect the dye results.
Without going up into my attic and finding my ol' college class notes, I think if anyone wanted to use natural dyes, you'd need a book from the library for reference.
You just can't take berries and dye cotton. It might stain for awhile, but not "dye". There is a difference. Then there are mordants that can be used to affect the way the material accepts the dye-stuff and makes it more permanent. But, while vegetable dying is natural and "green", it is not without future problems like fading in sunlight, etc.
It was a wonderful and fun course I took at Kent State in the late 1970's, called Weaving I (101) but called for much organization and (some) expensive dyes and large kettles for equipment, etc.... Take a class or at least find a good book on it. Good luck.