colors messed up after X screen lock (buster with xfce)

["Roland Winkler" <winkler@gnu.org>]

I am running debian 10 (buster with xfce).  Graphics works fine
initially.  Yet after an X screen lock, all colors are messed up.
The same hardware was previoulsy running fine when I was xubuntu 16.04.
What can be causing this?  Thanks!

Roland