The Centennial State. Colorado's official nickname is The Centennial State. Colorado became the 38th state of the United States in 1876 (one hundred years after the signing of our nation's Declaration of Independence).olorada-quarter.jpg. Colorado became the 38th state in 1876. Colorado's commemorative state quarter features the Rocky mountains, pine trees, and one of the state's nicknames: Colorful Colorado (public domain image on Wikipedia).