Borders above and below on iPhone 5 - colour query

Hi folks.

I've designed my apps for standard resolution displays (iPhone 3 and 4 etc), and I don't really have to upgrade them so they 'stretch' for the likes of the iPhone 5.  Anyway, because of this I understandably get the bars above and below my app.

When I tested this on my local device, these bars appeared black.  So it looked ok to be honest.  But when I submitted them via the AppStore and downloaded them, the bars above and below are now grey!  Just like the grey around the stage in Adobe Flash.  And it makes my app look pretty cheap.

Is there a way around this?  I'm thinking I'll just have to create a big black box with a hole in it 320 x 480 pixels in dimension and put it on one of the top layers.  But this seems a bit....hacky?  The stage color for my apps is currently set to white (not grey)

Any advice appreciated.