By the end of April, terror threats to the U.S. will no longer be described in shades of green, blue, yellow, orange and red, says an AP report.

The nation's color-coded terror warning system will be phased out beginning this week, according to the report. The officials requested anonymity to speak ahead of an announcement scheduled Thursday by Homeland Security Secretary Janet Napolitano.

The Homeland Security Department and other government agencies have been reviewing the Homeland Security Advisory System's usefulness for more than a year. One of the most notable changes to come: The public will no longer hear automated recordings at U.S. airports stating that the threat level is orange, the report says.

The Obama administration will take the next three months to roll out a replacement, which will be called the National Terrorism Advisory System, the report says. The new plan calls for notifying specific audiences about specific threats. In some cases, it might be a one-page threat description sent to law enforcement officials describing the threat, what law enforcement needs to do about it and what the federal government is doing, the report says.

When agency officials think there is a threat the public should know about, they will issue an announcement and rely on news organizations and social media outlets to get the word out.

The five-tiered color-coded terror warning system, created after the terrorist attacks of Sept. 11, 2001, was one of the Bush administration's most visible anti-terrorism programs. Criticized as too vague to be useful in communicating the terror threat to the public, it quickly became the butt of late-night talk show jokes.

The government hasn't made changes in the colored alert levels since 2006, despite an uptick in attempted attacks against the U.S. However, the government has changed security protocols since then based on threats. For example, new airport security measures were introduced after an effort to bring down a Detroit-bound jetliner on Christmas Day 2009.

Under that 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. Since the outset, the nation has never been below the third threat level, yellow — an elevated or significant risk of terrorist attack.

The use of colors emerged from a desire to clarify the nonspecific threat information that intelligence officials were receiving after the 2001 attacks.