Controls.pas里面这么说的，只有在XP支持皮肤的时候才透明，否则不行。
所以建议用label，别用StaticText了，因为那是窗口控件，都带背景的。
{ New TControlStyles: csNeedsBorderPaint and csParentBackground.
These two ControlStyles are only applicable when Themes are Enabled
in applications on Windows XP. csNeedsBorderPaint causes the
ThemeServices to paint the border of a control with the current theme.
csParentBackground causes the parent to draw its background into the
Control's background;
this is useful for controls which need to show their
parent's theme elements, such as a TPanel or TFrame that appear on a
TPageControl. TWinControl introduces a protected ParentBackground
property which includes/excludes the csParentBackground control style.
}
TControlStyle = set of (csAcceptsControls, csCaptureMouse,
csDesignInteractive, csClickEvents, csFramed, csSetCaption, csOpaque,
csDoubleClicks, csFixedWidth, csFixedHeight, csNoDesignVisible,
csReplicatable, csNoStdEvents, csDisplayDragImage, csReflector,
csActionClient, csMenuEvents, csNeedsBorderPaint, csParentBackground);
