I would use a white batt, not natural, since you have white fabrics in the top. A natural may make your whites look less white.

A white or neutral batting is not going to show through you backing.

If I have a lot of white in my top then I use white batting, otherwise I use the natural which is easier to find. I've never had a problem with it showing through on dark fabric.

I always use white batting with no problem of it showing through on black or dark fabrics. I bought a Hobbs black batting one time just to try it & I don't care for the black at all because of the feel of it. I do love Hobbs white batting though