I don't know if its possible to change the color of that black border line.
I developed a Command Button some months ago and I think you can change the border colors of it (I'm not sure). You can download a shareware version at my home page.
the black is a window thing..once an item gets focus you can tell which item has focus by the extra black around the item.
You can get around it by using an image control and loading it with your own picture of a button.
"A myth is not the succession of individual images,
but an integerated meaningful entity,
reflecting a distinct aspect of the real world."
___ Adolf Jensen