You can define a background color or use a graphic as a background for cell ranges in LibreOffice Calc.
Applying a Background Color to a LibreOffice Calc Spreadsheet
Select the cells.
Choose \<emph\>Format - Cells\</emph\> (or \<emph\>Format Cells\</emph\> from the context menu).
On the \<emph\>Background\</emph\> tab page, select the background color.
Graphics in the Background of Cells
Choose \<emph\>Insert - Picture - From File\</emph\>.
Select the graphic and click \<emph\>Open\</emph\>.
The graphic is inserted anchored to the current cell. You can move and scale the graphic as you want. In your context menu you can use the Arrange - To Background command to place this in the background. To select a graphic that has been placed in the background, use the NavigatorNavigator.