If I understand you correctly, you want an alpha channel.

I suggest you make a solid white PNG but make the white semi transparent using the PNG alpha channel. Set that PNG as a tile background to your table. I suspect that will let you see the background look white washed.

I've never tried anything like this before so if it works please let me know.

Problem though: I don't think MS Internet Explorer supports the alpha channel for PNGs properly. Try it in FireFox, it would work there I'm sure.

But if it doesn't work in IE...maybe you have to consider if it is really worth the effort. Test PNG transparency in IE before you start.