Yes, he would be considered a Resident of Colorado and also a Statutory Resident of DC. In the TurboTax interview, choose 'Full Year Resident' in the DC interview.
On the next page, he can choose 'Married Filing Separately on Same Return'.
Since you have TurboTax Desktop, you can subtract your non-wage income items manually on Schedule 1, if the interview screens don't prompt you.
CO will give credit for tax paid (or due) to DC, as you mentioned.
You could also prepare a MFS 'mock' Federal return to transfer to the MFS DC return.
Here's more details on How to File a Non-Resident State Return and Filing Separate States.
@netengler
[Edited 2/21/2024 | 12:10 pm]
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