Hmm...
The black looks good. If you choose that you just have to make sure you use exactly the same fabric as in the blocks, as not all blacks are the same!
And honestly, I'm not a fan of the orange (too light and girly in my opinion) or any shade of brown (wouldn't mix brown with black).
I still think the dark purple is gorgeous. A dark grey would look good, something like Kona Cotton Coal.