Colo. Const. art. XV, § 12
The general assembly shall pass no law for the benefit of a railroad or other corporation, or any individual or association of individuals, retrospective in its operation, or which imposes on the people of any county or municipal subdivision of the state, a new liability in respect to transactions or considerations already past.
Source: Entire article added, effective August 1, 1876, see L. 1877, p. 70.
Cross references: For ex post facto laws, see § 11 of article II of this constitution.