That's an image file on my iPad is called "FolderSwitcherBG@2x~ipad.png." A majority of the themes in Cydia do theme that part. Or, you can theme it yourself with Winterboard.
Just know that, when/if you theme it, the same image will show in your folders (background image) when you open them.
If you get a theme built specifically for the iPad, the odds are they have themed that image. For example, I am running the [paid] theme Carla and this is what my multitasking bar looks like:
As you can see, it's not linen AND it runs all the way across the screen with my iPad in landscape
Yes, I have bought some of these themes, the ones that get very many users happy and get good reviews.
But still I am not happy with them
My last themes I spent hard earned cash on, was BlackHaz hd and white Dreamboard theme.
The first was way too dark, almost unreadable for my old eyes - might be a winner among young folks
That shiny white dresmboard didnt work properly, and too difficult to mod.
This Carla looks very promising, light and bright, just to my taste