Cell-Selected-Color
This property allows you to set or retrieve the color of the selected cells when Selection-Mode includes grsm-cell-selection. Foreground and background color values are combined and therefore RGB colors are not supported. See "Color management" for further details.
This color is always visible, even when the Grid doesn’t have the focus.
 
Example - Set the colors for selected cells
procedure division.
...
  modify screen-1-gr-1 cell-selected-color 480
..