Reddit reviews Coral Snakes of the Americas: Biology, Identification, and Venoms

> In the United States, all coral snakes follow the 'red touch yellow' pattern

Occasionally they don't, and there are a couple of harmless species that do. However, once you hit Latin America, it's best to forget that dreadful "red-on-yellow" rule altogether.

This article discusses the subject in detail:

http://thevenominterviews.com/2016/06/02/mythbusting-coral-snakes/

In Latin America, the simple rules aren't reliable, and the reliable rules aren't simple. You would be looking at subtle differences in head shape, eye size and scalation.

For learning the local species, Janis Roze's Coral Snakes of the Americas is an excellent reference.