Thought I'd just like to share my thoughts on my experiences making graff and in recipe making.
I've probably made almost 30 batches now, its become kind of my regular thing. My main variant that I make, the recipe of which changes from time to time, is what I refer to as schwartzbeir graff. Basically dark but not roasty at all , fairly tart and a nice balance between malty and crisp, with a nice head. (I'll post my most recent recipe soon)
In general, especially for my purposes, I found the best way to incorporate the malt both in flavor and color was to mash the grain in the apple juice itself (I use a BIAB method). I realize the osmotic potential is way lower here so it doesn't raise the gravity as much as you would expect, but this is basically the only way that I've worked out to reliably get a dark color (adding even very dark wort to apple juice usually results in nothing darker than a nut brown ale)
As to grain I usually add a mixture of pilsener, munich malt, chocolate wheat malt (carafa II or III usually has a roastier flavor, this is sometimes labelled as midnight wheat) and flaked barley for head. The more munich you add the sweeter the final product will taste. Basically the same principles I've used here should be applicable to make graff in the style of other beer types by changing grain and mash characteristics.
I've had good success with a variety of hops, for me I like to add quite a bit more than the original recipe (usually I like noble hops) mostly because I think hops can compete rather than overwhelm the apple flavor. 2-3 oz for me is fairly subtle in a five gallon batch compared to what you can buy nowadays, even with some high alpha cultivars I've tried.
Mostly ditto comments of the people here on recommending clean beer yeasts. I use a kolsch yeast most of the time that balances well for my purposes. Safale US-05 is another great go to. Some of the other california yeast strains do a good job of adding floral estery character into graff that I like, but It's usually not what I'm going for so I thought I'd mention that. White labs cider yeast is phenomenal, if you like clean tasting stuff that yeast ferments pretty quick and clears very quick (seems to me like it precipitates in a powder and still ferments on the bottom quite a bit). In short, I think yeast choice in graff can make a big difference, so I'll let y'all have fun with that.
That's it for now, thanks Brandon O for getting so many going on this and making some great homebrew.