People cannot intentionally not notice it if they never knew it was there to begin with. It isn't noticeable for most because it is a color that can blend in with the sky and unless we have a reason to see it we don't. It's a fake horizon (not related to the now dead attraction). That isn't and never should be our focus. They knew that when they built it and it is an optical trick that still works from ages back.
What proves that point is that so many of us that complained and whined and bitched about it while it was being built can go to Epcot and never even once visually and consciously notice that it is there. Think about this crowd... if it were showing up like neon there would be an entire special category to register the complaints. If someone like an old Imagineer came on and explained that it is an intentional optical illusion, like the party room in HM, all of you folks would just fall all over yourselves in an effort explain how clever it was to do it that way.
That said, they could, I think, plant trees in front of it (if they haven't already) and over time the trees would hide the exterior just like they did with Haunted Mansion. Of course, depending on the angles and such, a hurricane, which has been known to happen in Florida from time to time, could wipe them all out and do other damage if the wind flow between the buildings is just right. I think that the way that the topographical area where Canada is elevated already would make that much more difficult also with the line of site being longer it is also less able to easily hide in the background. Considering all those things, I think it is amazing that it works to hide itself as much as it does. Even HM can be seen from some angle that has some distance and visual range.
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