Fluxbox is small and quite flexible window manager.  One of its great features is the ability to become pseudo-transparent. What pseudo-transparency does is that it produces effects, which are similar to the features offered by more heavier window managers like Gnome and Kde. Fluxbox does not however create any performance impact if its pseudo-transparency features are enabled.

To enable pseudo-transparency do the following.

1.Open Fluxbox root menu (the right click menu).

2. Navigate to Fluxbox menu –> Configure –> Transparency

3.  Click Force Pseudo-Transparency to enable it.

4. Set Focused Window Alpha (I have used 150).

5. Set Unfocused Window Alpha  (I have used 100).

6. Set Menu Alpha (I have used 150).

You will need to restart Fluxbox in order to see the changes.

Note. The actual menu entries and their names may be different depending on your configuration or Linux distribution.

To see how the pseudo-transparency looks with the settings I use: look   Blackdust-burned screenshots.