Bug 63420 [R21PRES] Flash on tab switch
bundles/org.eclipse.ui.presentations.r21/src/org/eclipse/ui/internal/presentations/R21BasicStackPresentation.java
* Returns the underlying tab folder for this presentation.
	 * 
	 * @return
	 */
	protected R21PaneFolder getPaneFolder() {
		return paneFolder;
	}
	/**
	 * Returns true iff the underlying tab folder has been disposed.
	 * 
	 * @return
	 */
	public boolean isDisposed() {
		return paneFolder == null || paneFolder.isDisposed();
	}
	/**
	 * Update the tab folder's colours to match the current theme settings and
	 * active state
	 */
	protected void updateGradient() {
		if (isDisposed())
			return;
		Color fgColor;
		Color[] bgColors;
		int[] bgPercents;
		boolean vertical = false;
		if (isActive()) {
			if (getShellActivated()) {
				fgColor = R21Colors.getSystemColor(SWT.COLOR_TITLE_FOREGROUND);
				bgColors = R21Colors.getActiveViewGradient();