What result are you trying to get ? This is the main point. If I understand what you have and what you try to get instead of what you have, maybe I could suggest something.
1) During boot the grey default screen color actually flickers before displaying
the user selected wallpaper.
2) When switching users the grey default screen also flickers on and off before displaying
the root or user selected wallpaper.
3) If I comment out PCManFM as the desktop manager and not use feh the grey color appears.
This is the only script I have:
# Set a background color
if which hsetroot >/dev/null; then
elif which esetroot >/dev/null; then
elif which xsetroot >/dev/null; then
test -z $BG || $BG -solid "#000000"
4) I've run it successfully in etc/xdg/openbox/autostart.sh on a different OpenBox distro
with 100% success turning the OpenBox default screen black forever. Now with PCL Openbox
you said we cannot run it there. Fine.
It must not be the right script to run in /root or /home for openbox/autostart.sh because
it doesn't work 100% there. It renders a black screen but turns grey again with usage.
All the other themes, colors, fonts, etc. are working OK when set OK.
Not a major problem but I thought it would be nice to learn how to do so and reduce some
some screen flicker at the same time.