diff -u b/core/modules/color/color.module b/core/modules/color/color.module
--- b/core/modules/color/color.module
+++ b/core/modules/color/color.module
@@ -284,7 +284,7 @@
 
   // Attempt to load preview HTML if the theme provides it.
   $preview_html_path = \Drupal::root() . '/' . (isset($info['preview_html']) ? drupal_get_path('theme', $theme) . '/' . $info['preview_html'] : drupal_get_path('module', 'color') . '/preview.html');
-  $variables['html_preview'] = SafeMarkup::checkAdminXss(file_get_contents($preview_html_path));
+  $variables['html_preview']['#markup'] = file_get_contents($preview_html_path);
 }
 
 /**
diff -u b/core/modules/color/src/Tests/ColorSafePreviewTest.php b/core/modules/color/src/Tests/ColorSafePreviewTest.php
--- b/core/modules/color/src/Tests/ColorSafePreviewTest.php
+++ b/core/modules/color/src/Tests/ColorSafePreviewTest.php
@@ -45,13 +45,14 @@
    * Ensures color preview.html is sanitized.
    */
   function testColorPreview() {
-    // Install the test theme
+    // Install the color test theme.
     \Drupal::service('theme_handler')->install(['color_test_theme']);
-
-    $url_object = Url::fromRoute('system.theme_settings_theme', ['theme' => 'color_test_theme']);
-
     $this->drupalLogin($this->bigUser);
-    $this->drupalGet($url_object);
+
+    // Markup is being printed from a HTML file located in:
+    // core/modules/color/tests/modules/color_test/themes/color_test_theme/color/preview.html
+    $url = Url::fromRoute('system.theme_settings_theme', ['theme' => 'color_test_theme']);
+    $this->drupalGet($url);
     $this->assertText('TEST COLOR PREVIEW');
 
     $this->assertNoRaw('<script>alert("security filter test");</script>');