How to remove the frame around desktop thumbed icon?

I use function Thumbnail, but there is always an unwanted frame around the thumbed icons:

I found the frame is related to
“Style * Colorset 0, HilightColorset 1”
If I change the colorset, the color of the frame will change. But the “border” is still unchanged.

How to remove the frame? Thx.

Style * IconBackgroundRelief 0

Solved. Thanks!