Can't help with Colombia specifically but on the wider topic of Latin America I highly recommend "Open Veins of Latin America".
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this was the first thing that came to mind
excellent book
Not sure that I have anything explicitly on Colombia.
You might enjoy Debray's Revolution in the Revolution, about Latam revolutionaries.
If you wanted some fiction, you might like Isabel Allende. Long Petal of the Sea is about Chile, I believe.
ProleWiki posted the following about the Shining Path: https://en.prolewiki.org/wiki/Library:The_CIA%27s_Shining_Path:_Political_Warfare
About the brutal role of imperialism in Latin America, you can find valuable information in the following books:
Dark Alliance: Movie Tie-In Edition: The CIA, the Contras, and the Crack Cocaine Explosion - Gary Webb
Killing Hope: Us Military and CIA Interventions Since World War II - William Blum
Open Veins of Latin America: Five Centuries of the Pillage of a Continent - Eduardo Galeano
The New Confessions of an Economic Hit Man - John Perkins
As for a book that talks specifically about Colombia, I have none that I can recall. However, I will check with some Colombian comrades to see if I can find any books that could help you with your investigation.
Ok, found some info!
El ruido de las cosas al caer – Juan Gabriel Vásquez
Los Ejércitos – Evelio Rosero
Río Muerto – Ricardo Silva Romero
Cóndores no entierran todos los días - Gustavo Álvarez
Some writing from Gabriel García Márquez are good
Also, as my comrade told me, this is about Marxism in Colombia -> https://repositorio.unal.edu.co/handle/unal/53470 It has a great historical analysis.