Comment 23 for bug 132833

"In my opinion, this is the best solution:

Replace this line in /etc/gdm/PreSession/Default

BACKCOLOR="#dab082"

With this:

BACKCOLOR=`gdmflexiserver --command="GET_CONFIG greeter/BackgroundColor $DISPLAY"`"

That did not work for me, however.
If I replace the line in /etc/gdm/PreSession/Default

 # Default value
  if [ "x$BACKCOLOR" = "x" ]; then
  BACKCOLOR="#dab082"
  fi

to

 # Default value
  if [ "x$BACKCOLOR" = "x" ]; then
  BACKCOLOR="x"
  fi

Then it obey the login manager colour settings.