Would something like this work?
% Set the figure color;
f = figure(...
'color',[0 1 0]);
% Add text box component.
txtbox = uicontrol(f,'Style','edit',...
'String','Enter your name here.',...
'Position',[30 50 130 20]);
% Grab the color from the figure, and set it as the backgroundcolor.
set(txtbox,'BackgroundColor',get(f,'Color'));
Of course it's not transparency, but at least some capability to match the background color. You can of course set the color via the set option to any prefered color as well.
HTH
