The symptom happens when I tried to connect from Windows 10 to Ubuntu laptop via the tightvnc viewer where the Ubuntu laptop is running tightvncserver
Solution:
$ sudo apt-get install gnome-panel gnome-settings-daemon metacity nautilus gnome-terminal
Add the following lines to ~/.vnc/xstartup
gnome-panel &
gnome-settings-daemon &
metacity &
nautilus &
[source]: https://askubuntu.com/questions/800302/vncserver-grey-screen-ubuntu-16-04-lts