I went into visual tropes a bit in the write-up on detective fiction tropes. Here's a little more detail.
First, though, I acknowledge that it may seem overly simplistic to group these tropes as binary forms. A bit of study will show that these binary relationships are the entry point to much more nuanced ways of looking at detective fiction, some of which I hope to elucidate here.
The inner ring:
Clarity/obscurity is probably the dominant trope in detective fiction. From it come numerous other tropes: vision/blindness, darkness/light, revelation/concealment. It's part of the language of the detective (and his sidekick, if he has one, Nora Charles being one of the delightful ones). It's part of the language of those observing the detective as well. Note that I would also accept arguments that revelation/concealment is the dominant trope, with clarity/obscurity as second. These tropes are important to each other and to the general narrative of detective fiction, and the ways that authors play with the tropes shaped that general narrative.
In True Detective, this trope is turned on its head (as it has been during most of the 20th century). Hart appears to be the "clear" one, yet in fact he's obscured because of his need to conceal his infidelities. The interesting thing about this deception is that it's insignificant, at least on this police force in this part of south Louisiana. Given what we see and learn about his colleagues (except for Cohle) on the force, Hart could confess all, and indeed does to Gilbough and Patania, and no one cares. There's no question about his having compromised ethics in his professional life as a consequence of his compromised ethics in his personal life. His infidelities do not matter. Hart is the one who more readily relates to the other investigators and policemen, the one who speaks the language of the police chief when political troubles arise from the Tuttle family and their task-force-for-hire.
Cohle's contrast with Hart could not be more stark. Cohle seems to be the obscure one, with complicated philosophical explanations of ontology, teleology, and epistemology that few understand. Cohle is treated as if he is obscured by his colleagues, including Hart; in terms of professional relationships, it probably does not matter much because Cohle was never going to fit in with his colleagues for much longer. In terms of personal relationships, we see one relationship deteriorate because of Cohle's difficulties in relating to others without becoming bored. Conversely, Hart is treated as if clear by his colleagues, when in fact he has much to hide--especially once he decides to beat up the two college boys with whom his daughter was caught having consensual sex.
Vision/blindness: Another highly important and frequently employed trope. Metaphors about sight and vision abound in detective fiction, and because they also abound in our day-to-day language, they seem even more natural. One thing to point out in True Detective is the scene in episode 4, "Who Goes There?", when Hart tells Gilbough and Patania:
You know the "detective's curse"--the solution was right under my nose, but I was paying attention to the wrong clues?
Hart's blindness, what he later refers to as "inattention," is in contrast with his willingness to see along the same lines as Cohle when it comes to the investigation. Hart's blindness is personal, not professional, and although it costs him his wife and family, it does not interfere with his ability to help solved the murders.
Like vision/blindness, darkness/light is another widely used trope in detective fiction. Lighting is important in many scenes in True Detective, two of which I will point out here: the flickering lights associated with the long single-take scene in the projects in episode 4, "Who Goes There?" and the dim lighting in Carcosa on the Childress estate. Flickering lights in general are associated with deception in True Detective; dim lights are associated with covert behavior and actions, eg, the dim light in Cohle's apartment when Maggie seduces him; fluorescent lights are associated with open deception, most strikingly in the police station; and sunlight is associated with revelation, trust, and clarity.
Revelation/concealment is also arguably the dominant trope in detective fiction. Here in True Detective, it appears in three important ways. One, the King in Yellow as a religious revelation. Without this, the murders would not have happened, or at least not to that degree. Two, concealment of the cult's activities as political concealment. Without this, the murderers are more easily found, and the cult is exposed. Three, the power to both reveal and conceal as political power. This appears in the form of the task force, which ostensibly is to investigate the murders but which in fact is set to obstruct Hart and Cohle's investigation.
Inevitably, visual tropes lead to the trope of the palimpsest, here where Hart and Cohle follow the footsteps and path of the criminal, losing it for a bit among the weeds and brush of the LeDoux encampment, but finding it again as part of Guy Francis's confession.