diff --git a/book.json b/book.json
index 43daee60..018ce0b3 100644
--- a/book.json
+++ b/book.json
@@ -7,7 +7,8 @@
     "pluginsConfig": {
         "uml": {
           "format": "png",
-          "nailgun": false
+          "nailgun": false,
+          "config": "monochrome"
         }
     }
 }
\ No newline at end of file