Good news and bad news. The good news is, when you choose a color (code) or pick a color, simply type in the word 'none'.
The bad news is, this doesn't work on all blocks. I just tried to change my Galleries block and it wont work.
So, go here -
http://www.imagefap.com/mydesign.php . Then next to
View other block: , you see the blocks you can change.