Monsoon chain gun question

[Harpss1ngh]

I'm currently fitting these compression fittings into my project, I have a quick question regarding the O-Rings. There's two O rings supplied with the fittings, am I correct in assuming the 2nd O-Ring is for the Barb side and not just as a spare? Doesn't make sense to me why there would be coloured O rings on the side screwed into a waterblock so I'm assuming that's the case

 

[OJ46]

Used these fittings on mine and just assumed the extra O-Ring was a spare... No leaks so can't have been too important!