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
public void updateMessage() {
		String message = currentPage.getMessage();
		int messageType = IMessageProvider.NONE;
		if (message != null && currentPage instanceof IMessageProvider)
			messageType = ((IMessageProvider) currentPage).getMessageType();
		String errorMessage = currentPage.getErrorMessage();
		if(errorMessage != null){
			message = errorMessage;
			messageType = IMessageProvider.ERROR;
		}
		
		messageArea.updateText(message,messageType);
	}
	/* (non-Javadoc)
	 * @see org.eclipse.jface.preference.IPreferencePageContainer#updateTitle()
	 */
	public void updateTitle() {
		messageArea.showTitle(currentPage.getTitle(),currentPage.getImage());
	}
	/**
	 * Update the tree to use the specified <code>Font</code>.
	 * 
	 * @param dialogFont the <code>Font</code> to use.
	 * @since 3.0
	 */
	protected void updateTreeFont(Font dialogFont) {
		getTreeViewer().getControl().setFont(dialogFont);
	}
}