Houston I have a problem

In the middle of installing two new sensors and I realised I had dropped a clanger,I had unplugged both sensors,separated the cables etc,Only then did I remember that I had not indentified the two sensor plugs,further thought and I realised that it is possible that the fitter who installed the previous pair could have crossed the plugs over anyway. The plugs on the loom are coloured red and blue but the sensor plugs are both white. Can anyone tell me which colour plug is which please? I do wish I had a wiring diagram. Mike

Oxygen sensor plugs 

Well with the help of FAQ I managed to deduct that the front sensor is the Blue plug. Mike