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
setShellSize(computedSize.x, computedSize.y);
				lastShellSize = getShell().getSize();
			}
		});
		Composite pageAreaComposite = new Composite(composite, SWT.NONE);
		pageAreaComposite.setLayoutData(new GridData(GridData.FILL_BOTH));
		GridLayout layout = new GridLayout(1, true);
		layout.marginHeight = 0;
		layout.marginWidth = 10;
		pageAreaComposite.setLayout(layout);
		
		Composite titleComposite = new Composite(pageAreaComposite, SWT.NONE);
		layout = new GridLayout();
		layout.marginHeight = 0;
		layout.marginWidth = 0;
		layout.verticalSpacing = 0;
		layout.horizontalSpacing = 0;
		titleComposite.setLayout(layout);
		titleComposite.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
		createTitleArea(titleComposite);
		
		pageContainer = createPageContainer(pageAreaComposite);
		pageContainer.setLayoutData(new GridData(GridData.FILL_BOTH));
		
		Label separator = new Label(pageAreaComposite, SWT.HORIZONTAL | SWT.SEPARATOR);
		GridData gd = new GridData(GridData.FILL_HORIZONTAL);
		separator.setLayoutData(gd);
		return composite;
	}