Yes that's because you have one image in the background; so the image comes in the background and not the color.
If you remove/comment the line
background-image: url(images/abc.gif);
you can see the cell overriding the row css.
If there is one image then it will have its own background colors, it can not be changed. You can only give borders as you have done.
Accept if I am right, otherwise give your query again.
I will help you.
Thanks...