Use of comma in a series

Posted by S. Ryan on February 20, 2003

I realize that the language does evolve and sometimes rules become blurred. I had always thought that a comma is used between all words in a series except when connected with "and." For instance, red, blue, yellow (no comma) and green lights. In a new textbook here in the U.S., the comma is used before the "and."
As in, red, blue, yellow, and green lights. Which is correct?