There is no longer support for 8 bit color depth in TigerVNC (see:
https://github.com/TigerVNC/tigervnc/commit/e86d8720ba1e79b486ca29a5c2b27fa25811e6a2);
using it causes a fatal error.

Submitted upstream at: https://github.com/canonical/lightdm/pull/265.

diff --git a/data/lightdm.conf b/data/lightdm.conf
index 0df38429..60e3e8b4 100644
--- a/data/lightdm.conf
+++ b/data/lightdm.conf
@@ -160,4 +160,4 @@
 #listen-address=
 #width=1024
 #height=768
-#depth=8
+#depth=24
diff --git a/src/x-server-xvnc.c b/src/x-server-xvnc.c
index 68340d53..27ca4454 100644
--- a/src/x-server-xvnc.c
+++ b/src/x-server-xvnc.c
@@ -127,7 +127,7 @@ x_server_xvnc_init (XServerXVNC *server)
     XServerXVNCPrivate *priv = x_server_xvnc_get_instance_private (server);
     priv->width = 1024;
     priv->height = 768;
-    priv->depth = 8;
+    priv->depth = 24;
 }
 
 static void
diff --git a/tests/scripts/vnc-command.conf b/tests/scripts/vnc-command.conf
index 0f1e25fd..335956d9 100644
--- a/tests/scripts/vnc-command.conf
+++ b/tests/scripts/vnc-command.conf
@@ -19,7 +19,7 @@ command=Xvnc -option
 #?VNC-CLIENT CONNECT
 
 # Xvnc server starts
-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=TRUE
+#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=TRUE
 
 # Daemon connects when X server is ready
 #?*XVNC-0 INDICATE-READY
diff --git a/tests/scripts/vnc-guest.conf b/tests/scripts/vnc-guest.conf
index 431bb244..ce2b97db 100644
--- a/tests/scripts/vnc-guest.conf
+++ b/tests/scripts/vnc-guest.conf
@@ -21,7 +21,7 @@ user-session=default
 #?VNC-CLIENT CONNECT
 
 # Xvnc server starts
-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=FALSE
+#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=FALSE
 
 # Daemon connects when X server is ready
 #?*XVNC-0 INDICATE-READY
diff --git a/tests/scripts/vnc-login.conf b/tests/scripts/vnc-login.conf
index cdfe17b8..f0d65b7f 100644
--- a/tests/scripts/vnc-login.conf
+++ b/tests/scripts/vnc-login.conf
@@ -21,7 +21,7 @@ user-session=default
 #?VNC-CLIENT CONNECT
 
 # Xvnc server starts
-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=FALSE
+#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=FALSE
 
 # Daemon connects when X server is ready
 #?*XVNC-0 INDICATE-READY
diff --git a/tests/scripts/vnc-open-file-descriptors.conf b/tests/scripts/vnc-open-file-descriptors.conf
index 753c84dd..e5d35730 100644
--- a/tests/scripts/vnc-open-file-descriptors.conf
+++ b/tests/scripts/vnc-open-file-descriptors.conf
@@ -21,7 +21,7 @@ user-session=default
 #?VNC-CLIENT CONNECT
 
 # Xvnc server starts
-#?XVNC-0 START GEOMETRY=1024x768 DEPTH=8 OPTION=FALSE
+#?XVNC-0 START GEOMETRY=1024x768 DEPTH=24 OPTION=FALSE
 
 # Daemon connects when X server is ready
 #?*XVNC-0 INDICATE-READY