I am using Qt Designer 4.0.1 on Linux, and when I change the background color or the color of pushbuttons, all text subsequently shows up in gray when I preview the form.
To change the colors, I am changing the palette from the Property Editor, and selecting the 3D Effects, and Background colors on the Edit Palette dialog. There seems to be no control there for the Foreground, ButtonText, etc. colors. There also seems to be no way to remove the palette, once I edit one. I am a Qt newbee, so maybe there is an easier way to set the colors.