I lived in two states (Colorado + Washington) in 2016, but only worked in one. Officially, I was only a resident of Colorado. Do I need to file two state returns?

I "officially" moved (got my driver's license and registered to vote) in January of 2017 even though my mailing address was changed in August 2016 (from Colorado to Washington). Should I file two state tax returns? If yes, would I file a nonresident return for Washington or for Colorado?