C.R.S. 18-18-406
https://www.colorado.gov/pacific/sites/default/files/Section%2016%20-%20%20Retail.pdf
In the state constitution:

“provided that the growing takes place in an enclosed, locked space, is not conducted openly or publicly”

openly and publicly are the (vague) key words

http://www.thecannabist.co/2014/07/02/six-months-legal-marijuana-sales-100-marijuana-questions-answered/14639/6/

And if it is more than 2 ounces it is serious.

http://www.criminaldefenselawyer.com/marijuana-laws-and-penalties/colorado.htm

It does not say open and public, it says open “or” public. Still more:
http://www.denvergov.org/sirepub/cache/2/wgdimdnzqdbkhc551mabn145/4543091121201509430868.PDF

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Here’s the thing.  I have this neighbor…

I don’t think it is legal.  If I call local law enforcement they will harass me.  If it is illegal they will not enforce it.