According to Director of Homeland Security Tom Ridge: “We introduced the Homeland Security Advisory System (HSAS), later called the ‘terror alert system’ to the nation in March [12] 2002. We settled on five levels represented by five colors: green (low risk), blue (general risk), yellow (significant risk), orange (high risk), and red (severe risk). In each case, specific measures were to be taken at airports and other public facilities.”
– Tom Ridge with Lary Bloom, The Test of Our Times, Page 99