How should I answer the question of residency Residency on Dec 31, 2019) when I sold my home and traveled for almost a year?

You will probably be considered a full-year CO resident until such time as you set up a permanent residence in another state...and change your Driver's lisc. and Car registration to that new state (and register to vote there too will help )  Until that time, you are still a CO resident, and a part-year CO resident only in the year you actually establish yourself, more-or-less permanently, in a new state...as-of the date you actually do set up in that new state...not before..

There are special considerations for full-time RV'ers who never alight in one place for long...but even they have to establish a residence state, set in one state, even if they move about for many years.

The question is, where is your domicile?  Your domicile is the place you call home. It is the place where you have significant family, social, and business ties. Such as, your pharmacy, your doctor, your attorney, your voter registration, your library card, your favorite mechanic, your church, and so on.  You can be traveling and not own a house or have an apartment lease, but still have a domicile, probably where you most recently lived.  You only ever have one domicile at a time, no matter how many residences you might own.

As @SteamTrain suggests, your domicile was probably Colorado even though you sold your home and were traveling.  Colorado will certainly assume that your domicile was Colorado and that you owe full year income tax, unless you can show that you established a domicile elsewhere.

I can't find anything that comes straight out and addresses this specific situation. But from everything I read in the CO tax regulations, you are a full time CO resident until you establish residency outside of Colorado, and that residency has to be established in accordance with the residency requirements of the location where you establish that new residency.

It's also noted in a few of the regulations that I read that the requirements you meet for residency outside of CO must be those requirements required for tax purposes if that location so defines requirements for such. For example, residency requirements for a college to offer a student in-state tuition rates are rarely the same as those requirements for state tax purposes.

Colorado Regulation 39-22-103(8)(A) specifically states:

Once a person’s domicile is established in a state, it will continue to be the person’s domicile until the person establishes domicile in another state.

https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=6070&fileName=1%20CCR%20201-2

Therefore you must file as a full-year CO resident until you establish a new permanent home - a new domicile - in another state.   Living on the road or in temporary lodging such as hotels does not constitute establishing a new domicile.

I'm sure the rules would be similar for any state in which you had established a prior domicile....even if you can't find the particular regulation that handles the situation.

I can't see any state allowing one to exit their domicile state, and suddenly declaring themselves to be either stateless, or domiciled in a different state, without them actively taking steps to establish a domicile of some type in that new state.  The mind boggles at the chaos that might ensue.

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The only exception I know of is recent  national legislation that allows the civilian spouse of a military member to declare they are a resident of the military member's HOR/SLR, without actually going to that state to establish a domicile.