[xvilka]

Shameless plug - you can add also my tiny transset rewrite and enrichment - set_opacity[1]. It allows making X windows translucent, without any interaction required. Wrote it more than a decade ago, but still should be usable. This is how you can use it:

set_opacity -o 0.5 -i `pgrep gkrellm`

There is also a patched[2] xcompmgr with the colored shadows support:

xcompmgr -fF -I-.002 -O-.003 -D6 -cC -t-5 -l-6 -r5 -R 1 -G 0.5333 -B 0

[1] https://github.com/XVilka/set_opacity/

[2] http://xvilka.narod.ru/files/xcompmgr-1.1.2.tar.bz2