[plt-scheme] A classic: Changing the background color

Hi all,

I have a strong feeling this has been asked before, but Google was for 
once unhelpful.

I have a frame with a few horizontal panels, a canvas, and an editor. 
Some components
have white background, but most including all "filler" space have a grey 
background.

Is there a way to change the background of the frame% in which 
everything is placed?

-- 
Jens Axel Søgaard