Green is the hardest to use.
The others can feed off an out of control emotion and goad the user into less rational actions.
Willpower requires the most focus and discipline to harness.
(Not that I think they thought that deeply into the rainbow of fruit flavored magical wishing rings, but it makes sense in my head.)
They may have thought about it given how Green arrow is so cynical he cant make the ring work without almost having a stroke and that apparently the ring wouldn't light up at all recently for Constantine.