@oantolin And Dover Editions! "This is a permanent book".
Just picked one off the shelf -- Introduction to Graph Theory -- it falls open about 3/4 of the way through where the four-color theorem is introduced.
*I've* never gotten that far in that book. Treats in store!
Are you referring to _Introduction to Graph Theory_ by Richard J. Trudeau (https://store.doverpublications.com/products/9780486318660)? If so, do you recommend it?
I've been wanting to learn graph theory for a while, and this seems like it could be a good place to start.