It doesn't matter if it is green or blue. Both are the same. The colour is only to make the right assembly in the car.
On my 4/4 I had a pre cat sensor and a post cat sensor on the original exhaust. After change to a Librands system I only need the pre cat sensor.
It doesn't have a post cat sensor. But the problem was the cable on the pre cat sensor was too short for the new position of the cat in the exhaust,
but the not needed post cat sensor was. So I assembled them together, green mother to blue father by cut of the noses of the housing.
And everything worked as well as before. So there are now differences because of the colour. Also the sensors were exactly the same.
The colour is only to protect miss assembly with the wiring harness in the car.
