You can choose the background when playing a puzzle and also of each tray independently. A good background will result in a clean view of the puzzle pieces, choose a pleasant one and also make sure the pieces can be easily distinguished.

To activate the background settings press  B 

The background is compound of two colors and a texture. Choose the two colors by just clicking in the two large boxes of colors and additionally tune the intensity with the slider at the right.

The  Random  button will choose at random a new set of colors based on the contents of the image: it will try to find among the colors that contrast in the color predominant in the image in order to achieve a good separation from the pieces. You can then fine tune it if you feel necessary or press random again to see another possibility. Below random there are  Undo / Redo  buttons to go back in the history of colors chosen for the case you can go back to some choice you skipped.

The slider  Contrast  allows increasing the intensity of the texture, the more to the right, the texture will be visible more clearly.

Below the colors there are the available textures. You can choose any of them by clicking on it. 

Alternatively to a texture, you can set an  Picture  as the background. This can make puzzles more difficult but if you use the  Colorize  option you can achieve unique, clear and pleasant backgrounds.  Zoom  will reduce the size of the image used so the background will be a tile of the picture.  

Setting a picture on the gift puzzles is an additional nice way to pass photos to the receivers of the gift puzzles.

As the option Colorize applied to a picture can produce interesting variations, you can save it if you like: Right click the mouse on the zone of the textures and it should appear a pop-up menu with the option  Save current background as image 

 Favorites : You can save the settings you like better or use more in the slots in the Favorites. Right click one of the slots to save the current background so it will be avilable later in other puzzles. To use one of the favorite backgrounds saved previously you just have to click it.

Each change in the background options will be immediately visible on the screen so you will see the result of the changes you make.

The option  Program's default  allows setting a constant background in the context you are, for example, if you check that option while you are setting the background on a puzzle, the next puzzles you start will have that background independently of other settings.

Notice that you can also set a background on the gallery (press the key B to access it and check  Program's default  so it's used the next times you run the program).