[Saphire]

Sorry about that. I should have explained.

To resize the image go to Image then canvas size, I gave it 2 centimetres in height and width, this gave a white border all the way round. Then I re-cropped the image to centralise it.

I then used the magic wand to pick the border. Rather than use a bucket fill which would leave a flat border, I used the clone tool to clone the sky into the new border. Deselect the area and then use the patch tool to tidy things up.

To change the sky colour I used the magic wand to get the sky, it was set for 5 pixels so I didn't take any of the plane.
I then used the Gradient tool with the foreground darker than the background. Place a line from the top to the bottom of the image this gives a good graduation of the two colours.
Finishe.