GreenLaguna: add a posibillity for changing the background color of the panel for dark ambiance,
useful for a transparency panel with a dark DE background.
update GreenLaguna README
Merge pull request #35 from NiceandGently/master

 GreenLaguna: add a posibillity for changing the background color of the panel for dark ambiance,  useful for a transparency panel with a dark DE background.