It is more of a dark blue than a dark grey. I agree, the instructions were incorrect: you need to put the wings on first.
The zippered fabric backing was attached with staples so close to the edge of the fabric that the fabric easily just ripped off.  Also the pull of the zipper did not have a stopper to keep it from sliding completely off the zipper.  So instead of having this extra yardage of fabric just hanging from the back of my headboard I ended up cutting it off.
That being said, the blue color is acceptable to me, the upholstered fabric is lovely, it fits my queen bed, and the whole thing is sturdy and it looks nice.