If arrested you have the right to an attorney. If you don't have one, one will be appointed to you (and paid for by the government). There is a presumption of innocence and you can expect a speedy trial.
The most common legal situation that travelers find themselves in involves drugs. In 2012, Colombia’s Constitutional Court decriminalized the possession of small amounts of cocaine (one gram or less) and marijuana (20 grams or less) for personal use, but that doesn't mean it's a good idea. Although you cannot be criminally prosecuted, police may still give you a hard time and you may be ordered to receive physical or psychological treatment depending on your level of intoxication.