Hi, I know there are a lot of discussions about this grey screen but I tryed all the solution I found searching in Google and I still have this grey screen when I connect to my Raspberry-Pi 3.
Here is my Xstartup code in /root/.vnc/

#!/bin/sh

xrdb $HOME/.Xresources
xsetroot -solid grey
#x-terminal-emulator -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &
#x-window-manager &
# Fix to make GNOME work
export XKL_XMODMAP_DISABLE=1
/etc/X11/Xsession

I start a new connection in this way: vncserver :1 -geometry 1280x720 -depth 24
When I edit the Xstartup file I also kill the connection and reopen it.
I really try all the Xstartup solution I found in Google but I still have this grey screen.
I'm using TightVNC Server in the Raspberry with Kali Linux 2.1.2 and TightVNC Viewer in my Windows computer.

When I was using Raspian I didn't edit the Xstartup because I had no problem so I don't know if it's a Xstartup problem or what.
Thank you.