Wired:

In either case, the rainbow-like coloring system is ending come April.

This isn't exactly surprising news; here's a senior Homeland Security official, last November:

The goal is to replace a system that communicates nothing with a system that communicates precise, actionable information based on the latest intelligence to law enforcement, the private sector and the American public.

RE: Color-Coded Terrorism ‘Threat Level’ Advisory System Ending | Threat Level | Wired.com