diff --git a/docs/assets/nature.css b/docs/assets/nature.css
index a663be2..f1e9316 100644
--- a/docs/assets/nature.css
+++ b/docs/assets/nature.css
@@ -158,9 +158,9 @@ div.body h6 {
 div.body h1 { border-top: 20px solid white; margin-top: 0; font-size: 225%; color: #EEEEEE; background-color: #6f8c93;}
 div.body h2 { font-size: 140%; color: #EEEEEE; background-color: #6f8c93; }
 div.body h3 { font-size: 120%; color: #2C001E; background-color: #accbd3; }
-div.body h4 { font-size: 100%; color: #EEEEEE; background-color: #accbd3; }
-div.body h5 { font-size: 100%; color: #EEEEEE; background-color: #accbd3; }
-div.body h6 { font-size: 100%; color: #EEEEEE; background-color: #accbd3; }
+div.body h4 { font-size: 100%; color: #EEEEEE; background-color: #accbd3; color: #000000}
+div.body h5 { font-size: 100%; color: #EEEEEE; background-color: #accbd3; color: #000000}
+div.body h6 { font-size: 100%; color: #EEEEEE; background-color: #accbd3; color: #000000}
  
 a.headerlink {
     color: #333333;
diff --git a/ldapcherry/exceptions.py b/ldapcherry/exceptions.py
index c249d76..da37cbc 100644
--- a/ldapcherry/exceptions.py
+++ b/ldapcherry/exceptions.py
@@ -196,6 +196,16 @@ class UserDoesntExist(Exception):
             " in backend '" + backend + "'"
 
 
+class UserAlreadyExists(Exception):
+    def __init__(self, user, backend):
+        self.user = user
+        self.bakend = backend
+        self.log = \
+            "user '" + user + "'" \
+            " already exists" \
+            " in backend '" + backend + "'"
+
+
 class GroupDoesntExist(Exception):
     def __init__(self, group, backend):
         self.group = group