I actually don't know anything about acrylic or PETG staining, Ive never worked with either to know how they act, and I probably won't for the foreseeable future.
I think with the plasticizer-free tubing, like I have, it gets foggy because it's porous and can absorb water, and given time to dry out it will return to its clear state with maybe the exception of the yellowish tint. Which i assume, is due to contact with UV sources of light; in my case, the sun.)
With older plastizer based tubing, it leeches the plasticizer into the coolant which then cakes on the tubes, rez, rads and in the water blocks, giving it a milky look, hurting performance leading to lots of cleaning.
Now one odd thing I've seen is when mixing different colors of UV tubing,where green was leeching into the blue tubing cause it to appear teal from the outside but was actually turning the blue tubing green. Even more bizarre was that the Pastel White never saw any changes or color shifts. Warning: Spoiler! (Click to show)