As everyone is discussing the danger levels of color code alerts and preparedness, I wondered what exactly each color code means and what activities would be triggered. There doesn't seem to be a list of what civilians should be doing in response to a code alert, but I did find this information from an email from the Emergency Email Network.
The entire message is at this link Click here, but in part it says:

                                                                   Low Condition
                                           Green

Low risk of terrorist attacks. The following Protective Measures may be applied:

       Refining and exercising preplanned Protective Measures
       Ensuring personnel receive training on HSAS, departmental, or agency-specific Protective Measures; and
       Regularly assessing facilities for vulnerabilities and taking measures to reduce them.

                                       Guarded Condition
                                             Blue

General risk of terrorist attack. In addition to the previously outlined Protective Measures, the following may be
applied:

       Checking communications with designated emergency response or command locations;
       Reviewing and updating emergency response procedures; and
       Providing the public with necessary information.

                                       Elevated Condition
                                           Yellow

Significant risk of terrorist attacks. In addition to the previously outlined Protective Measures, the following may
be applied:

       Increasing surveillance of critical locations;
       Coordinating emergency plans with nearby jurisdictions;
       Assessing further refinement of Protective Measures within the context of the current threat information;
       and
       Implementing, as appropriate, contingency and emergency response plans.

                                        High Condition
                                           Orange

High risk of terrorist attacks. In addition to the previously outlined Protective Measures, the following may be
applied:

       Coordinating necessary security efforts with armed forces or law enforcement agencies;
       Taking additional precaution at public events;
       Preparing to work at an alternate site or with a dispersed workforce; and Restricting access to essential
       personnel only.

                                        Severe Condition
                                             Red

Severe risk of terrorist attacks. In addition to the previously outlined Protective Measures, the following may be
applied:

       Assigning emergency response personnel and pre-positioning specially trained teams; Monitoring,
       redirecting or constraining transportation systems;
       Closing public and government facilities; and
       Increasing or redirecting personnel to address critical emergency needs.