1) Place oversized button (no image yet) on panel with a non-standard background color - Everything works, colors look ok, button colors and text, etc

2) Now add an image to the button.

The background color of the panel now shows through the button and no matter what size I make the image, I can't get the image to fill the whole button to hide the panel background color showing through. I can almost fix this by overriding the default background color property of the button but this property also slightly changes the background JUST outside the button so it doesn't look good.