Well, black interior is almost right. My reference book (Verlinden) on the AH64 does indeed show that the interior is in various shades of black. In particular, the cockpit floors are, in fact, a very, very dark green with black heel boards. Some of the vertical panels alongside the seats also have a dark green tinge to them.
I personally think that an all black interior does not look right, and some experimentation with very dark greens, extremely dark greys as well as black and some careful drybrushing with 'dust' colours will give a much better, lived-in look which suits military helicopters better. From a distance, it might well look black!!
That's where the art side of modelling can lift an otherwise boring, all-black interior.
Hope this helps.