This post is a slight deviation from my previous post with a different end result. For simplicity I will start at the beginning again.
1. Open your image in Photoshop.
2. Click the Channels Tab.
3. Hold down the CTRL key and single click on the RGB channel, this will load the luminosity as a selection.
4. Press the "Create New Channel" icon on the bottom of the Channels dialog - this will create a new Channel "Alpha 1".
5. Set your background colour to white and press CTRL+DEL a few times to fill the selection with white.
6. Select your brush tool and set your foreground colour to White.
7. Press CTRL+D to deselect the selection.
8. Paint white on all the areas you would like to be white in the final image.
9. Press CTRL+I to invert the channel and then double click on it to load it as a selection.
10. Select the Marque Tool from the toolbox and with the Alpha Channel selected move the selection into the new document where you want the background (you can move it when the little rectangle is displayed).
11. Create a new Layer and select a foreground colour you would like to use, I'm using a dark blue. Press ALT+DEL to fill the selection with the colour.