I think everything looks just fine as is but here is my take.
I don't like generic gravel because all the multi-colored rocks can take away from the fish/plants/driftwood/background. I find it makes the tank a little busy looking.
That being said, I really do like black gravel. I just set up a new 75 and the black gravel really accentuates the plants and fish colors in there.
For me its either black grav or sand.