Umbriel . Uranus II . Umbriel [UM-bree-ul] is the darkest satellite of Uranus. It is about the same size as Ariel and has about the same density. The surface appears to be old with large craters and does not change much from one location to another. Near the top is a puzzling bright ring called the fluorescent cheerio . ... Dark regions are represented as red and bright regions are represented as blue. The two white regions are bright ejecta from two fresh craters. ...