Change table view ( tableview style grouped ) background color?

I am developing an iPad application in which I need a table view ( style grouped ) having background color as clearColor.

My problem is

[self.tableView setBackgroundColor:[UIColor clearColor]];

works well if the table view style is plain but when I switch to group table view the background color does not changes it stays gray in color.

FYI: the contentview background color of tableviewcell also does not change.

Is this a bug in iPhone-sdk or I am doing something wrong.

solved:

simply do:

[self.tableView setBackgroundView:nil];

Hope this helps.