Hello,
I'm using Roundcube for more than one year, and I really enjoy using it.
I recently added some features to my installation, so I made a patch. Maybe you could be interested in it.
The patch answers to the #1457360 ticket Actually I posted some code in this ticket, but I think it is more comfortable for you in a patch, got from the last svn revision.
I'm not an artist and I don't know how to make transparency with the gimp, so only "act" pictures are made, not "pas" and "sel".
Cheers,
Mat