Hello. You can't create a LAYOUT with a transparent background, but, if you have FileMaker 13 and greater, you can create a popover that is transparent.
A colleague logicurio wrote a great blog post and made a tutorial about this technique. Your popover is transparent and 'slides' in and out of the layout you're on. Once the thing is set up on one layout you can use it everywhere.
I used this technique a few times. It is a great way to show the navigation of a system.