Sounds a bit similar a game I've played in swedish 'Grinden' (= gate). In english it becomes something like:
The game starts by a sentence stating one item which can pass through the gate and one which cannot. And an invitation for the person investigate what can go through the gate.
"A goblin can pass through the gate but a leprechaun can not."
Then it goes:
The objective is to figure out the rule which allows items to pass through the 'gate'. This can be stated explicitly or be left to be figured out.
Then you ask whether or not various things get through the gate until you figure out why.
The standard rule for first time playing is to allow only things which starts with a letter in the word 'Gate' but only if said in the correct 'sequence'. The asker cycles through the word 'Gate' in their head and keeps track of which letter is currently allowed.
Does an Elephant get through? - No (needed something on G)
Does an Elephant get through? - No (needed something on a)
Does an Elephant get through? - No (needed something on t)
Does an Elephant get through? - Yes (needed something on e)
And so it goes until the 'victim' figures out the rule.
So try asking her 'Green' many times and see what periodicity it has if it comes up with different results. Though the format seems to suggest some other rule, hard to guess with the limited information.
[Edit: *** i'm frustrated, I really don't understand why it is so hard to put things in spoilers? Why do I need the dots in between why doesn't it just work to have one single long spoiler. Someone who knows please edit and explain in comments]
