I'm not sure this will be helpful or not. I have wondered the same thing. How do I change one little bit of a particular theme. I looked thru my directory structure one day and found config type files related to themes. These files had lines similar to Conky: argb value = ___ or opacity =____ or color = ____. That sort of thing. I haven't tried changing any of these entries, can't remember where the heck I found the files. I'm just guessing that you need a desktop that supports transparency, like KDE/Kwin and you need to find these files to change the values, if they are even available.
i5 3570k, ASRock z77 Extreme 4, 8 Gb Ripjaws 1600, Antec 430w psu, HVR 1600 tv tuner, custom case- marble top, oak face. Carver & DCM Time Window sound system. Mint 14 KDE.