After updating xfce4-terminal to version 0.8.0 pseudo transparency does not work anymore. It prints the warning that my window manager (Xmonad) does not support compositing and disables the opacity slider. I do not have a compositor running. For now I downgraded to 0.6.3. Pseudo transparency works fine there. OS: Arch Linux GTK: gtk3 3.22.1 gtk2 2.24.31
Unfortunately, there's no way for a gtk3/vte3 terminal to become transparent other than using compositing feature of a WM. Please also see bug 12906. *** This bug has been marked as a duplicate of bug 12906 ***