diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
index 2c2ac3a..8c3798a 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
@@ -3,6 +3,7 @@
 namespace Drupal\FunctionalJavascriptTests;
 
 use Drupal\Tests\BrowserTestBase;
+use Zend\Escaper\Escaper;
 use Zumba\Mink\Driver\PhantomJSDriver;
 
 /**
@@ -109,7 +110,10 @@ protected function assertJsCondition($condition, $timeout = 1000, $message = '')
    *   The file name of the resulting screenshot. If using the default phantomjs
    *   driver then this should be a JPG filename.
    * @param string $background_color
-   *   (optional) Background color name.
+   *   (optional) Background color name. To use the default background color set
+   *   to NULL, however this can result in completely black screenshots if the
+   *   theme does not have a background color. This string is escaped by
+   *   \Zend\Escaper\Escaper::escapeJs().
    *
    * @throws \Behat\Mink\Exception\UnsupportedDriverActionException
    *   When operation not supported by the driver.
@@ -119,7 +123,8 @@ protected function assertJsCondition($condition, $timeout = 1000, $message = '')
   protected function createScreenshot($filename, $background_color = 'white') {
     $session = $this->getSession();
     if (!empty($background_color)) {
-      $session->executeScript("document.body.style.backgroundColor = '" . $background_color . "';");
+      $escaper = new Escaper();
+      $session->executeScript("document.body.style.backgroundColor = '" . $escaper->escapeJs($background_color) . "';");
     }
     $image = $session->getScreenshot();
     file_put_contents($filename, $image);