Changing background color for a box widget

["Mike Martin" <redtux1 googlemail com>]

Is it possible to alter the background color for a box widget. I am
not having a lot of luck

To explain I have a dynamically created hbox added to a vbox inside a frame.

In this hbox I have two widgets a label frame (a file name) and a remove button.

I would like the background to be white so there is some contrast.

I have tried with rc files and modify_bg but it doesn't seem to take.

Any ideas?