If you get blindness mob effect while looking at a portal in a distance, you'll find the world all black, while the inner side of the portal frame and the remote world still visible.

Maybe night vision effect causes the same issue but it's hard to test it because the portal itself glows.

The behavior is quite normal (because the remote world is rendered by "another camera") and maybe difficult to fix, but should not be intended. It is weird if we think about it using common knowledge (without any technical knowledge).