This Google Script converts the currently active Google Spreadsheet into a square grid of randomly colored boxes using hexadecimal numbers. Credit 五味田和則

The random colors are generated using a JavaScript method - Math.ceil(Math.random()* 0xFFFFFF).toString(16)`. Also, since the value of the cell is the same as the color code, you can copy a cell to copy its color code.

function colorCodes() {
  var sheet = SpreadsheetApp.getActiveSheet();
  for (var i = 1; i <= 100; i++) {
    sheet.setRowHeight(i, 20);
    sheet.setColumnWidth(i, 20);
    for (var j = 1; j <= 100; j++) {
      var colorcode = Math.ceil(Math.random() * 0xffffff).toString(16);
      sheet
        .getRange(i, j)
        .setBackground("#" + colorcode)
        .setValue(color);
    }
  }
}