To add a bit to the previous answers:
If your employer cannot withhold CT taxes for you, then you must make quarterly estimated tax payments to CT. Scroll down to the "Estimated Tax Payments" section of this CT tax document for details:
https://portal.ct.gov/DRS/Individuals/Resident-Income-Tax/Tax-Information#EstTaxPay
If you are certain you will do no work within Colorado, then be sure your employer does not withhold CO income tax from your pay.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
