The fig holds shrinking qualities, which is why it is used in Shrinking Solutions. This potion has the ability to shrink the drinker into a infant form, and also works on animals and items. Neville's batch of Shrinking Potion also turns his toad into a tadpole, showing the age reversal techniques in animals.
The colour of the solution is important in indicating the safety of the mix: if the solution is green, it is drinkable. However, if it is orange, it is poisonous. This explains why the potion is only brewed by third years at Hogwarts.
(A successfully brewed Shrinking Potion. Image from one of the Harry Potter video games. Shrivelfigs and other content in this post is the creation of J.K. Rowling)