It has experience level equal to the LATs that reconsituted it. In case of fire teams (most common) it means green, in case of assault teams it mean line.
Actually, not quite. Experience level for squads is not tracked DURING the mission. Yes, when Litter Teams or Fire Teams attempt actions, they do it at 'Green' level (-1 card), but this is solely for the purpose of performing Actions. When reconstituted, the squad is still the level it was on the log at the start of the mission. It is not intended that we track a changing experience level for each squad throughout the mission. Note that the rules state that it is at the END of the mission when LAT steps are actually demoted to Green. And at this point Assault teams become Green steps, too (they ARE LATs) even though DURING the game they function as Line quality.
In short, do not track squad experience during the mission. It only changes at the end when Green steps (or veteran) are absorbed to replace losses.