Bug 56637 [Preferences] DialogMessageArea image is too large
Is the background color of the error shown by DialogMessageArea to be changed? Or do you intend to leave it as it is right now? The error message looks a little out of place in the current implementation (being surrounded by white space).
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferenceDialog.java
getTreeViewer().getControl().setFocus();
		}
	}
	/**
	 * Display the given error message. The currently displayed message
	 * is saved and will be redisplayed when the error message is set
	 * to <code>null</code>.
	 *
	 * @param errorMessage the errorMessage to display or <code>null</code>
	 */
	public void setErrorMessage(String newErrorMessage) {		
		if(newErrorMessage == null)
			messageArea.clearErrorMessage();
		else
			messageArea.updateText(newErrorMessage,IMessageProvider.ERROR);
	}
	/**
	 * Save the last known tree width.
	 * 
	 * @param width the width.
	 */
	private void setLastTreeWidth(int width) {
		lastTreeWidth = width;
	}
	/**
	 * Sets whether a Help button is available for this dialog.
	 * <p>
	 * Clients must call this framework method before the dialog's control
	 * has been created.