var $cells = $('table.table td');
for (var i = 0; i < $cells.length; i++) {
  var $cell = $cells.get(i);
  if (!$cell.hasClass('table__cell--disabled')) {
    $cell.css('background', $cell.data('colour'));
    ...

$('table.table td').each( function() {
  $cell = $(this);
  if (!$cell.hasClass('table__cell--disabled')) {
    $cell.css('background', $cell.data('colour'));
    ...
});