Pretty sure it's bugged. It's meant to be white when you can place it and yellow when you can't but it's yellow 90% of the time.
I noticed that they increased the distance from a wall or structure allowed when compared to KZ2. In that game you could pretty much place it very far back against a wall but here it seems to require 2 or 3 times as much space on all sides to construct it -- likely to still allow enemies the opportunity to get behind and deconstruct it.
It stinks sometimes as I would have found amazing places to construct them but I don't have enough space.