Is there a way to edit an excel file with TestComplete?

Use Interior.ColorIndex to change background color of a cell

function testWriteExcel() {
  let excelObject, excelWorkbookObj, excelMainSheet, sheetName;
  try {
    sheetName                 = "test";
    excelObject               = Sys.OleObject("Excel.Application");
    if (excelObject == null)
      throw Error("Excel n'est pas installé !");
    excelObject.Visible       = false;
    excelObject.DisplayAlerts = false;
    excelWorkbookObj          = excelObject.Workbooks.Open("c:\\temp\\test.xlsx");
    excelMainSheet            = excelWorkbookObj.Sheets.item(sheetName);
    excelMainSheet.Cells.Item(3, 3).Value2 = "Test";
    excelMainSheet.Cells.Item(3, 3).Interior.ColorIndex = 6;
    excelObject.AlertBeforeOverwriting         = false;
    excelObject.Application.ActiveWorkbook.SaveAs("c:\\temp\\testcolor.xlsx");
  }
  catch(e) {
    Log.Message("Erreur durant la mise à jour Excel", e.message, pmHigher, system.logWarning);
  }
  finally {
    if (excelObject != null) {
      excelObject.Application.ActiveWorkbook.Close;
      excelObject.Quit;
      excelObject      = null;
      excelWorkbookObj = null;
      excelMainSheet   = null;
      killProcess("EXCEL", false, false, 10);
    }
  }
}