Question about tables – alternating fills

Question

Apologies, but I new to the world of Tables and, as an exercise only, I am trying to create following:
I have a to create a table 21 columns wide (they're very narrow) and nine rows deep
I want theTOP ROW ONLY to have an alternating fill of 50% black; the first column being white then 50%; then white and so on.
Producing the alternating fill is (obviously) very easy, but I am struggling to limit it to the top row only.
Can anyone advise on the best approach

Answer 1

Actually it is not working. I copied the text of the script, inserted into Adobe Extended Script Tool, saved it as *.jsx and added into InDesign User Scripts.
I create a table and ran the script and it returned an error
It might be missing something in the script.
Here it is what I took from that post:
app.doScript(function() {
  // Put Swatch names in here, many as you like:
  var rowFills = [
    "Blue",
    "None",
    "Black"
  // Put Percentages in here, again many as you like:
  var rowTints = [
    50,
    0,
    25
  table = app.selection[0];
  if (table.hasOwnProperty("baseline")) table = table.parent;
  if (table instanceof Cell) table = table.parent;
  if (table instanceof Column) table = table.parent;
  if (table instanceof Row) table = table.parent;
  if (table instanceof Table)
    var startAt = table.headerRowCount;
    var numRows = table.rows.length-startAt-table.footerRowCount;
    for (r=0; r<numRows; r++)
      table.rows[startAt+r].fillColor = app.activeDocument.swatches.item(rowFills[r % rowFills.length]);
      table.rows[startAt+r].fillTint = rowTints[r % rowTints.length];
  } else
    alert ("Yeah, come to think of it you were actually nowhere near a table, werentya?");
    exit();
}, ScriptLanguage.JAVASCRIPT, undefined, UndoModes.ENTIRE_SCRIPT, "Alternate Table Fills");
Anyway, thank you for idea.