The rule is: the state you live in gets to tax all of your income regardless of where it comes from, and a state gets to tax income earned or located within it.
So both CA & CO get to tax your CO rental income. The good news is that TT/Calif will prepare a tax credit for some or all of the CO tax on the income that both states are taxing to help prevent double taxation. Prepare the nonresident CO return first, then the resident CA return.
