Hi Ramakrishna, it doesn't look like you'll be able to directly override the color of that enclosing <td> element since it's hardcoded, but you can override the background color of the element contained within the cell like this:
.mpcalendartitle { background-color: black !important; }
You may still see a silver border around the title (I did in my test), but there might be a way to hide that (i.e. cover it up) by playing with the padding or margin settings for the mpcalendartitle selector class. Joe D. is much more of a CSS guru than I, so hopefully he'll have a full solution for you.
Jamie