Blue
Ravenous Bugblatter Beast of Traal
What this sounds like to me:Emphasis min. Yes, that. "What you can see" includes the result of a passive check.
In regards to the "whole range of the d20" @billd91 talked about, there is nothing wrong with walking into a room, looking around and upon perceiving there are dark corners or places to hide deciding to actively search for hidden enemies. That is an action, and it has consequences.
Character walks into a room. Passive perception is used.
Character takes an action to actively look around. DM ignores the action, undermining player agency.