I would definitely go with the black and gray, and feel free to add a little bit of primary colors in it, here and there.
I have a daughter that is really into black, and over the years I've collected various black, white, gray fabric, and copy pic of quilts on the internet hat use those colors, many times with a touch of some other color.
Adding a touch of the bright pink, with bright blue, green, yellow, to me, would be lovely
I hope this shows, to me, this could very well be a 'baby' quilt:
http://0.tqn.com/d/quilting/1/0/Q/U/...nnin_quilt.jpg