This is Caesium-137. Cs-137 has a physical half life of 30.17 years, it is the most common radioactive form of caesium and a byproduct of the nuclear fission processes in nuclear reactors and nuclear weapons testing. Over 30.17 years this will change colour roughly 1520 times per day until all the 16,777,216 colours within the RGB colour spectrum are cycled through. Over 30.17 years it will also change frequency at an average rate of 1.7 times per day, cycling through all frequencies within the human range of hearing.

When the cycle has completed it will expire.