Report Manager - Options Screen - Additional Report Settings
Use the Additional Report Settings feature by clicking on the 3 vertical dots below the Form selection field or by pressing [F8] from the Report Settings Screen to adjust the Highlight Lines parameters (style, color, width). The available options are "None", "Gray Bars" (highlight color may be adjusted), and "Top Lines" (highlight color and line width may be adjusted). The highlight is added only to the last (or most detailed) band(s) of the report since the upper bands are already separated by the details.
See:
Report Manager Contents