Good morning Elishiva,
You have a background image for the hover effect on that menu,
That image isn't there so, instead of your image, an "image not found" .gif loads instead. That's the black that you're seeing.
The gray seems to be coming from a gradient background ... also on the hover but I can't seem to tell if it's on the anchor or the li.
Check to make sure your path and spelling are correct for menu-hover.png.