Black background in conky widgets are known issue now a days, so I come up with some solutions to fix these issues. You may install the conky you love but get black shadow with conky, it is because of Compiz window decoration in Unity and other desktops who uses compiz. If you are in any other desktop and getting same shadow so there is another solution is to change conky mode within the conky script.
Articles by "conky black background"