- Contents are visible from the outside and lighting is flattering to said objects. Hence a glass front. A triple glazed argon or krypton gas filled window would do the trick. The function of this is to make the contents more appealing. Presentation of both the contents and the interior of the fridge should have significant influence on your likelihood to eat fruit.
- The temperature of this refrigerator would most likely be higher than your standard fridge which are usually set at about 34 degrees. Luckily this has been researched heavily. Humidity should be studied too.
- Maybe there are separate sealed compartments for different fruits and there's an ethylene gas filter that keeps fruit from ripening - or the reverse. Say you want avocados to ripen quicker so you put them with ripe apples (and this is all figured out in an algorithm that you merely have to press a button to get near ideal settings) in one compartment.
It'd be interesting to design a few dozen prototypes then run a double blind study and see if it did in fact effect participants consumption of fruit. You could take what you learned and tweak the design to try to maximize the influence it had.
I'm aware this would add yet another device to the kitchen. As an alternative maybe this could just be a shallow compartment within the door of a standard fridge. An operable window to the outside could serve much of the function as what was mentioned above.