If you knew anything about cinematography (which 99.9% of people within LUA Scripting do), you’d know about color correction. Color correction basics pertain to the act of bringing out more pure blacks and pure whites, and doing so creates a saturated look. After you have attained these pure black and white levels (which unfortunately you could never gauge in GMod due to a lack of any (to my knowledge) known waveform monitors) you can then manipulate the color scheme by adding blues (most cinematic generic touch), greens, or reds, or a combination thereof.
You can pull off these effects by eye alone, but you’ll just have to take the time to get the feel for the cinematic color levels. Look for slight saturation, then add color tones.
I noticed you mentioned “desaturated” in your OP. The reality is, as I said above, these are pure black and white levels, with toned down colors. It’s somewhat of a desaturation, but not entirely.