You are considered a part-year resident because you moved into the state in 2018. A part-year resident is an individual who was a Colorado resident for only part of the tax year. This includes a person who moved into Colorado during the tax year with the intention of making it their home and a Colorado resident who moved out of Colorado during the tax year with the intention of making their home elsewhere. The link below has information from the Colorado Department of Revenue that you may find useful.
https://www.colorado.gov/pacific/sites/default/files/Income6.pdf
