I often hear people asking how to install compiz, beryl on Fluxbox at IRC during the period when 3D desktop effects caught the crowd’s attention. And the answer is definitely NO! you can’t mix beryl with Fluxbox.
Beryl is a combined window manager and composite manager written in C using OpenGL to provide acceleration. Fluxbox is also a window manager, so you can not use beryl and fluxbox together.
If you are looking to have eye candy of true transparency and fade effects on Fluxbox, here I present you a composite manager call xcompmgr. Refers to Transparency Howto at Fluxbox wiki, you need to install transset-df as well to turn a window into transparent. With Fluxbox 1.0rc3 ( or maybe earlier version), Fluxbox have build in true transparent support as well as pseudo transparency.
You are allow to set the opacity ( as they wrote as alpha value ) on root menu, focus and unfocus window.
More Here .