C.R.S. § 39-22-403

(1) In the case of a nonresident estate or trust, the tax imposed by section 39-22-104 shall be apportioned in the ratio of the Colorado-source federal taxable income to the total federal taxable income, both modified as provided in section 39-22-104 . (2) Colorado-source federal taxable income of an estate or trust means: (a) Its share of the Colorado-source federal distributable net income as determined in section 39-22-404 ; and (b) Its share of any Colorado-source income, gain, loss, and deduction recognized for federal income tax purposes but excluded from the definition of federal distributable net income of the estate or trust as determined under section 39-22-109 , as in the case of a nonresident individual, and modified as provided in section 39-22-104 .