Well, if you'll take notice, (but who really reads those damned credits anyway?), there will always be a credit for someone known as the "color timer".BS! I'm 20y broadcast engeneer and around 10 MCR (Master Control) engeneer, know everything about video audio standards in all formats including QC. I saw the 40min docu how the episode was shot, and ther is light enough on the set , for obvious CINEMATIC REASON they decided to tone it down and it is too dark, the black is crushed beyond resnoble explanation. I belive the raw material is completly OK and all this darkness was edited in post production. I understand what they wanted to express but that was really way too much, and belive me I know how setup corectly 2 of my LG screens one led +HDR the other OLED Dolby Vision, it's too freaking dark if you play with brightness or contrast you just make it worse, either way grayish and the colors get washout or as it should be but then it is 75% of the time so dark with some extreme bright spots (fire sources) wich is very annoying, no balance at all, I call it slappy ****ery job and HBO/GOT team should take in account it is ment for TV /streaming and the Cinematic part doesn't really fit in. In other words they ****ed up massivly from post production and QC.
Herewith my Google search results to the question, "what does a movie color timer do".
As you already know, movie stock is color negative, and the process of balancing the color in the final positive transparency, is very similar to color negative printing on paper, save for a special machine used to flip the negative positive, without a test printing need being done.
My other point is this. In reference to "available contrast", black is always black, but the maximum contrast available is always dependent on the maximum white level, or "absolute brightness".
The lower the maximum incident light, the closer it is to black in F-stops or exposure value. Consequently the less contrast which can be realized in the scene.
Photoshop measures this on a 0 to 255 scale, representing absolute black to absolute brightness, or 8 photographic F-stops. Should the maximum brightness be less that 255, Photoshop can stretch it out to full brightness, at a severe sacrifice in intermediate values.
In simpler terms , if you only have 4 F-stops of light level above black, you can either tolerate the low contrast available, or you can add contrast artificially, at the expense of lost shadow detail, and washed out highlights.
The techniques used in architectural photography, such as using very log exposures to capture existing lighting in the scene, and then lighting up the area with massive doses of flash with a secondary short exposure are well beyond merely impractical for motion picture work. Trying to light a movie set by firelight alone, would obviously present the same types of difficulties
But you probably know all that.