try handling the TableControlDrawCellDisplayText event and formatting the value there.
private void gridGroupingControl1_TableControlDrawCellDisplayText(object sender, GridTableControlDrawCellDisplayTextEventArgs e)
{
if(e.Inner.Style.CellType == "ColorEdit")
{
e.Inner.DisplayText = ((Color)e.Inner.Style.CellValue).ToArgb().ToString("X");
}
}