After years of ridicule on late night TV, the Department of Homeland Security is replacing color-coded terrorist threat alerts with public warnings that are more black and white.

Officials said Wednesday that they are scrapping the five-color system, which was created in the frantic months after the terrorist attacks of Sept. 11, 2001, because the alerts typically said little about the supposed threat or what authorities were doing to lower the danger.

Most importantly, studies showed that the public paid little heed to the much-mocked warnings. The level never dropped below “”elevated,”” and had not changed since 2006.

Starting April 26, written alerts will warn the public of an “”elevated”” threat or a more specific “”imminent”” threat. The bulletins will include details about a potential attack and steps that members of the public or law enforcement can take to help reduce the risk.

The color alerts have “”faded in utility,”” said Janet Napolitano, the secretary of homeland security, “”except for late-night comics.””

In February, for example, Conan O’Brien unveiled a five-tiered Nicholas Cage Terror Alert System on his TBS show, “”Conan.””

Whether the new National Terrorism Advisory System will get any more respect remains to be seen.

“”Any alert system is only as good as the intelligence that goes into it,”” said Frank Cilluffo, a former homeland security adviser to President George W. Bush.

“”This is an imperfect business,”” Cilluffo said. “”Risk communications is more of an art than a science.””

Giving out too much information could spread panic or tip off a terrorist cell that it has been infiltrated, said Rick Nelson, a homeland security expert at the Center for Strategic and International Studies, a Washington-based think tank.

“”The government will always be struggling with how much information to give without having a negative effect,”” he said.

Homeland security officials will disseminate the new alerts through the press and social media sites. The bulletins will ask local police and the public to be on the lookout for vehicles or behavior that may be part of a terrorist plot that the government is tracking. Alerts could be directed at airports or subways, or may urge people in a specific city to take shelter in their homes for a short time.

Alerts will be issued for two weeks unless intelligence agencies determine that the threat remains high enough to extend the warning. The goal is to “”get us away from cascading alerts that never seem to disappear,”” Napolitano said on a conference call with reporters.

Under the old system, green signified the lowest risk and fire-alarm red the most dire. A red alert was issued only once, on Aug. 10, 2006, when British authorities disrupted a plot to detonate explosives on airliners bound for the United States.