...
>> l.MarkerHandle.EdgeColorData(4) = 10
to 
You'll need to add a listener to change the transparency when the figure is resized, see comments in above thread.
Printing
export_fig is good for most figures. However, it does not do transparency.
Here is a way to copy to the clipboard a figure with transparency.:
set(gcf,'InvertHardCopy','off'),print -clipboard -dbitmap -r72
This may be helpfuul, haven't tested it:
http://undocumentedmatlab.com/blog/screencapture-utility