pdf.js change background color

var url = '//cdn.mozilla.net/pdfjs/helloworld.pdf';

PDFJS.workerSrc = '//mozilla.github.io/pdf.js/build/pdf.worker.js';

var loadingTask = PDFJS.getDocument(url);
loadingTask.promise.then(function(pdf) {
  var pageNumber = 1;
  pdf.getPage(pageNumber).then(function(page) {
    console.log('Page loaded');
    
    var scale = 1.5;
    var viewport = page.getViewport(scale);

    // Prepare canvas using PDF page dimensions
    var canvas = document.getElementById('the-canvas');
    var context = canvas.getContext('2d');
    canvas.height = viewport.height;
    canvas.width = viewport.width;

    // Render PDF page into canvas context
    var renderContext = {
      canvasContext: context,
      // Use transparent background!
      background: 'rgba(0,0,0,0)',
      viewport: viewport
    };
    var renderTask = page.render(renderContext);
    renderTask.then(function () {
      console.log('Page rendered');
    });
  });
}, function (reason) {
  // PDF loading error
  console.error(reason);
});