That sand bed looks VERY deep. It's too late now since you've already layed the substrate, but a friend of mine is heavy into planted tanks, and he uses a mixture of miracle grow/PFS, layered, with the MG on the bottom, for all his tanks. It's always worked good for him. Since you are just sticking with sand though I don't see the problem as long as you use root tabs, and possibly liquid ferts like flourish. You could have even used a single bag of flourite for substrate. Nutrients, and looks natural. Damn the stuff is initially dirty though.
I'd do the back black, and as far as the tone of the pfs, it might look bright now but if you heavily plant it, and maybe accent it with a few river rocks to scape, it'll all blend together.