Colo. Rev. Stat. § 32-11-612
Any person filing a written complaint, protest, or objection on any one or more specific grounds as provided in section 32-11-611, shall have the right within thirty days after the board has finally passed on such complaint, protest, or objection by resolution, as provided in section 32-11-611(3), or as provided in section 32-11-614(1), to commence an action or suit in any court of competent jurisdiction to correct or to set aside only such a determination of the board on any such specific and written complaint, protest, or objection; but thereafter all actions or suits attacking the validity of the preliminary plans, any preliminary estimate of cost, assessment plat, other proceedings, and any maximum amount of benefits shall be perpetually barred.
C.R.S. § 32-11-612