Now looking at the left side of the screen you will see the tools palette. If for some reason it does not appear, go back to the Window drop down menu and make sure a check mark appears by the "Tools" selection.
If there is not a check mark, simply click on tools under the Windows drop down menu and the palette should appear.
On the palette, look about 3/4 of the way down and you will see two colored squares which overlap each other.
Then just a little bit above the the squares on the right side of the palette, you should see an eyedropper. Touch on it with your cursor. Now when you place you cursor over photo 1, it should take the form of an eyedropper. Click on the photo at various points and look at the effect on the left colored square. It should change colors each time you select a color with the eyedropper.
For the moment, choose the brightest white you can find on the picture which seems to be down near the bottom of the Alley's sleeve.
(There are over ways to do this but this is the simplest for this purpose.)
Once you have chosen the brightest white. Look back at the colored squares and you will see a "two-ended arrow" to their top right which allows you to toggle between the two squares. Touch the toggle switch and make certain the white you have selected appears in the lower right square (which is your background color).