College dependent out of state, what state tax returns?

I am a NE resident, my son (21) goes to school full time in CO.  He changed his drivers license from NE to CO this summer and for 2019 has only earned income in CO from a part time job.  He is still my dependent per tax rules as I provide more than half of his support and he is a full time student and will be claimed as a dependent.  The question is on turbo tax his residency as of Dec 31- do we put CO since he has his license there and goes to school/worked there or for tax purposes is it still NE?  If it is CO then does he still need to file a NE state return since he was a resident here for part of the year even though he earned no income in NE for the entire year?  If his residency is NE then does he need to file both CO and NE state returns?   Thanks in advance