Colorado Revised Statutes Title 29. Government Local § 29-8-130. Civil action--grounds

(1) No civil action shall be brought or maintained to enjoin the collection of assessments or otherwise test the validity of assessments levied under this article except upon the following grounds:

(2) Every person whose property is subject to such special assessment and who fails to appear during the public hearings on said assessment to raise his objection to such assessment shall be deemed to have waived all objection to such assessment, except objections on grounds specified in subsections (1)(a) and (1)(b) of this section. Any action brought under this article shall be commenced within thirty days after the passage of the assessing resolution or else be thereafter perpetually barred. Any such action shall be given preference in the courts of the state. If such action is unsuccessful, the courts may order the plaintiff to pay the costs thereof, and, in its discretion, may require a bond in a sufficient amount to cover such costs at the commencement of such action. The burden of proof to show that such special assessment or part thereof is invalid, inequitable, or unjust shall rest upon the party who brings such suit.