To develop these themes you need to look at the relationship between Caliban and Prospero. Caliban represents colonialism, since he was colonized and slaved by Prospero. Notice that he works for Prospero, and he was taught the language by Prospero. The passing of the language, and the fact that Próspero considers Caliban inferior, prove his condition as a Colonized man.
Prospero, on the other side, represents Imperialism. He considers himself the ruler and a superior person. He tries to exercise his power in the rest. You can see this in the orders he gives not only to Caliban, but also to Ariel. He even exercises his influence on his daughter. Clear examples of this are his passing of the language to Caliban, and his blessing to Miranda's romantic relationship.