Continued from page 1

Former Homeland Security Secretary Tom Ridge has said the use of colors emerged from a desire to clarify the nonspecific threat information that intelligence officials were receiving after the 2001 terrorist attacks. The goal was to put the threat in terms the public could understand.

“And most importantly, it empowers government and citizens to take actions to address the threat,” Mr. Ridge said in March 2002 when, as Mr. Bush’s homeland security adviser, he announced the birth of the system.

Each color signaled specific security measures to be taken at airports and other public places. From the beginning, Mr. Ridge said, officials knew the system would become the target of critics.

Late-night TV host Conan O’Brien chimed in just days after the announcement.

“Earlier this week, Homeland Security Adviser Tom Ridge announced a new color-coded warning system. A color-coded system to keep the public informed about disasters. Seems like a good idea,” Mr. O’Brien said. “Yeah, apparently red is the highest alert, and it means Dick Cheney is about to eat a mozzarella stick.”

As part of her review in 2009, Ms. Napolitano solicited comments from the public about the current system. Some of those commentators likened the color-coded system to the boy who cried wolf. Others criticized it for not following the natural color spectrum. Others wanted the system to be based on numbers as opposed to colors and to mirror the weather alerts familiar to communities across the country.

Under the current system, green, at the bottom, signals a low danger of attack; blue signals a general risk; yellow, a significant risk; orange, a high risk; and red, at the top, warns of a severe threat. The nation has never been below the third threat level, yellow — an elevated or significant risk of terrorist attack.

While the colored descriptors haven’t changed in eight years, the government has modified how it uses them. The government departed from blanket warnings in 2004 when it raised the threat level for the financial sector in New York, New Jersey and Washington, D.C. Previously, warnings would have applied across the country.

The terror threat to the U.S. continues to change, but the color of the threat is the same as it was in 2006: yellow for the country as a whole and orange for the aviation sector.