Warning: file_get_contents(/libraries/colordialog/plugin.js): failed to open stream

this error is fixed with the next patch

diff --git a/src/Plugin/CKEditorPlugin/ColorDialog.php b/src/Plugin/CKEditorPlugin/ColorDialog.php
index 31f02f1..04e14c0 100644
--- a/src/Plugin/CKEditorPlugin/ColorDialog.php
+++ b/src/Plugin/CKEditorPlugin/ColorDialog.php
@@ -20,9 +20,9 @@ class ColorDialog extends CKEditorPluginBase implements CKEditorPluginContextual
    * {@inheritdoc}
    */
   public function getFile() {
-    $path = '/libraries/colordialog/plugin.js';
+    $path = 'libraries/colordialog/plugin.js';
     if (\Drupal::moduleHandler()->moduleExists('libraries')) {
-      $path = libraries_get_path('colordialog', TRUE) . '/plugin.js';
+      $path = libraries_get_path('colordialog', FALSE) . '/plugin.js';
     }
     return $path;
   }

This patch is located here
https://www.drupal.org/files/issues/colordialog-file-get-content-2929415-1.patch