Plug-in should set foreground as well as background color

###@###.### pointed out that we set the background color of the EmbeddedFrame containing the applet, but not the foreground color. This can result in surprising behavior where we paint white on white for some test cases. We should probably set the foreground color as well. Currently we obtain the background color from the GrayBoxPainter, but there is no way to query the foreground color, so that would need to be added as well.