In period one, actors can choose as many options as they want from a given set, with no limit. In period two, they have the chance to refine the set, if they want, with most selecting some subset that is small than the original. No new option that was not selected in period one can be chosen in period two.

I want to test whether they have a preference for green options in the first period. Then, I want to test if their preference for green stays the same, increases, or decreases.

Code:
set seed 1000
clear all
set obs 25
generate actorid = _n
expand 100
bys actorid : generate choiceid = _n
generate period1chosen = runiform() < 0.3
generate period2chosen = runiform() < 0.2 if period1chosen == 1
replace period2chosen = 0 if period2chosen == .
gen green = (choiceid < 25)
The first analysis is obvious reg period1chosen green.

The second analysis to get at changes in preference is less clear. reg period2chosen green seems wrong.