So, I'll just say this up front, and most here already know it. I'm not a liquid cooling guy. I don't particularly favor it, and that's ok. It's perfectly fine that some do and I HAVE build some of them for people who wanted them. However, I DO do a lot of plumbing. Both residential and commercial using copper, pvc, and have many years of working with older systems and systems that half and half meaning you end up with dissimilar metals throughout the plumbing circuit and we KNOW that those are eventually going to see galvanic corrosion so we try to eliminate as much of it as possible, when possible.
Sometimes it's not possible because there is lead, clay, black iron or steel pipe that is part of the original plumb job and is encased in concrete through the foundation or in other areas of the property. These are the ones that typically see external signs of galvanic corrosion with the green scaling and discoloring you are talking about. And if you can see it on the outside then it's much worse on the inside usually.
Since those loops typically use additives to inhibit that sort of electrolytic reaction AND since for the most part it's possible to at least mostly eliminate dissimilar metals in the loop, it would be a lot less likely that you'd see anything like that on the outside. I've used plenty of exposed copper heat pipe air coolers over the years that contain liquid agents inside the heat pipes for the heat transfer process and none of them has ever exhibited those signs of galvanic corrosion and discoloring.
I think as long as you kept the loop clean and refreshed periodically to ensure that the additives were still effectively inhibiting that kind of reaction and used only similar or same metals, that wouldn't be likely to happen. I have tens of feet of copper pipe that have been sitting in the rafters of one of my garages for many years and they all look like they did when they came off the shelf at the supply house. And those are stored in a somewhat humid environment so I doubt there'd be any level of humidity inside your case that could even potentially be a factor, if it even COULD be a factor.