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
if (hHint != SWT.DEFAULT)
				y = hHint;
			return new Point(x, y);
		}
		public void layout(Composite composite, boolean force) {
			Rectangle rect = composite.getClientArea();
			Control[] children = composite.getChildren();
			for (int i = 0; i < children.length; i++) {
				children[i].setSize(rect.width, rect.height);
			}
		}
	}
	
	private static String lastPreferenceId = null;
	
	private static int lastTreeWidth = 150;
	public static final String PREF_DLG_IMG_TITLE_ERROR = DLG_IMG_MESSAGE_ERROR; 
	/**
	 * Title area fields
	 */
	public static final String PREF_DLG_TITLE_IMG = "preference_dialog_title_image"; 
	static {
		ImageRegistry reg = JFaceResources.getImageRegistry();
		reg.put(PREF_DLG_TITLE_IMG, ImageDescriptor.createFromFile(PreferenceDialog.class, "images/pref_dialog_title.gif")); 
	}
	/**
	 * The current preference page, or <code>null</code> if
	 * there is none.
	 */
	private IPreferencePage currentPage;