Transparency is not available as a standard feature in the FeedWind setup screen but it is quite easy to implement. Once you have copied your HTML snippet from the setup screen, you can edit the code using a code editor or notepad.exe and replace any of the color codes with "transparent"
So for example, to get the background to become transparent, the entry:
rssmikle_item_bgcolor: "#FFFFFF"
would be changed to:
rssmikle_item_bgcolor: "transparent"
This also works for other elements which have a Hexadecimal color code for example such as #343AEE or #FFAACC. Just replace the color code qwith the word "transparent" and then publish the page and you will see the relevant elements of the widget will become transparent.