Setting a Background color using FlexReportDesigner is quiet easy. A background color in FlexReport can be set for Fields, Sections, and Sub-sections. The background colors can be Solid or Gradient.

The following image shows a Report header without any background:

To set a background to the Report Header:

1. In the Design mode, select the Header section of the report.
2. From the Properties window, click the drop-down next to Background property. The color palette opens.
   
3. Select a color for the background. You can choose color from the tabs - Web, System, Custom, and Gradient.
4. Preview the report.
   
5. You can also set Gradient - Linear or Radial - for the background. For obtaining a Gradient, switch to Design mode.    
6. Select the Header section of the report.
7. From the Properties window, click the drop-down next to Background property. Go to Gradient tab and edit the settings from the options available as shown:
   
8. Specify the gradient as Linear. You can also drag the slider to change the start and stop for the gradient.
9. Preview the report. The Report Header now looks as follows: