I have been asked about the feasability of using Persona images as Fast Dial Background

How can I get the Themes picture as background in FD?

There is an obvious immediate problem with this idea
The size of the persona images is 3000px wide x 200px high

This is not really the shape of the fast dial background.

You would have to decide if you wanted to tile these images as background or find a large version of the background and use part of it.

please see here and here

Perhaps try as a test saving this persona image to your PC and then loading as a background image into fast dial: (click on image to expand)

http://www.getpersonas.com/static/img/Persona_Header_LABS.jpg

Let us first see if you can see the image.
Best to tile the background.
You should then see a background made up of strips.

Once you have got that one working, you can play around...

(I have tested with this image.
It does work fine in tiled mode)

here is a gallery:
http://digitizor.com/wp-content/plugins/wordpress-toolbar/toolbar.php?wp...

I thought I could see that when choosing transparent in FDs preferences. But this only gives me a white background. What am I doing wrong?

the background colour only shows when there is no image.

If you have a small image loaded as background in centered mode, you may not see it easily unless you go into tiled mode.