The contrast of dappled light and shadow cast through the hulk by the setting sun provides natural camoflauge for anything inside the wreck, which is itself subdivided by bulkheads, machinery and debris, and sand dunes.  It would actually be less distracting in complete darkness, for those who are able, although anyone without darkvision would become more hampered.<br/><br/>For their part, the mules seem unconcerned, their attention entirely focused on whatever food and water they are given.<br/><br/>