Find the following in the suckerfish.css file which came with the plugin and remove the bit in red, that should create a transparent menu:
[code:289b2mp4]#suckerfishnav li:hover ul, #suckerfishnav li li:hover ul, #suckerfishnav li li li:hover ul, #suckerfishnav li.sfhover ul, #suckerfishnav li li.sfhover ul, #suckerfishnav li li li.sfhover ul {left:auto<span style="color:red">;background-color:#bbb;</span>}[/code:289b2mp4]
If that doesn’t work, then let me know and I’ll have a closer look.
EDIT: Actually, that probably wont work by itself. I’ll make sure you can easily make such corrections in the next version.
For the current version, you will need to hack the php file that came with the plugin too. Find where the code above (or similar) is in the plugin and remove the bit about background-color from it.