O2 Sensor query

[CarbonTC]

Hi, can anyone here tell me the difference between the blue and the green plug for O2 sensors? I need to replace my old ones for my 04 V6 and I dont know the difference.
Samples shown below:

Thanks.

 

[lincoln00]

maybe before and after cat.... look under car and see

 

[Quik LS]

the green are upstream, the blue are downstream (before = upstream / after = downstream the cat).

 

[CarbonTC]

i cant see the color because is to old and even thou i cleaned it with paper towel I still not able to see the color

 

[lincoln00]

look at the different part numbers when ordering... they should be able to tell you what O2 is pre and post..