How to inverse font color based on cell's background Color in Google Apps Script?

//https://stackoverflow.com/questions/70491148/how-to-inverse-font-color-based-on-cells-background-color-in-google-apps-script
//https://stackoverflow.com/a/70491346/10789707

function onEdit(e) {
  r = e.range;

  if(r.getSheet().getSheetName() == "colors"){ //the sheet I want to apply this to is called colors
    var rows = r.getNumRows();
    var columns = r.getNumColumns();
    var colors =  [] //this is our 2 dimensional array of colors in case you copy and paste a large amount of colors

    for (var i = 1; i <= rows; i++) { //go down each row
      var row = [] //create a new row array to clear the old one when we go down a row
      for (var j = 1; j <= columns; j++) { //then go across each column
        row.push(r.getCell(i,j).getValue()) //put together the row of colors
      }
      colors.push(row); //insert our row of colors so we can go down the next row
    }

    const fontColor = lum([111, 22, 255]);
    const fontColorsRow = new Array(columns).fill(fontColor);
    const fontColors = new Array(rows).fill(fontColorsRow);

    r.setBackgrounds(colors) //batch update in case you update many colors in one copy and paste otherwise it will be very slow

    r.setFontColors(fontColors);
  }
}

function lum(rgb) {
    var lrgb = [];
    rgb.forEach(function(c) {
        c = c / 255.0;
        if (c <= 0.03928) {
            c = c / 12.92;
        } else {
            c = Math.pow((c + 0.055) / 1.055, 2.4);
        }
        lrgb.push(c);
    });
    var lum = 0.2126 * lrgb[0] + 0.7152 * lrgb[1] + 0.0722 * lrgb[2];
    return (lum > 0.179) ? '#000000' : '#ffffff';
}