SMART datagrid v.1 > Classes > GridStyleSheet
If specify ColumnGroup.childSummariesVisible as false, the header cell of column group will be displayed in grid summary header instead of header of columns which have been contained in column group, and it is the default Style Set about these cells.
grid.setStyles({
header: {
summary: {
group: {
background: '#200088ff'
}
}
}
});