I just made an Imperial Black IPA (IBIPA?). I used chocolate wheat to get to 55 SRM. I milled that wheat to flour. It's black now, I don't expect it to get any lighter. High hopes for this beer. If it turns out, I'll post the recipe.
To the OP, I'd second the sinamar idea. That should do it. Does Beersmith have that in the ingredients somewhere?