In humanities essays, lists are generally run into the text rather than set vertically. A colon is often used to introduce a run-in list:

Chimamanda Ngozi Adichie has written four novels: Purple Hibiscus, Half a Yellow Sun, The Thing around Your Neck, and Americanah.

But no colon is used before a list when the list is the object of the verb that introduces it:

Chimamanda Ngozi Adichie’s novels include Purple Hibiscus, Half a Yellow Sun, and The Thing around Your Neck.

The list is the object of the verb include.