Based basically completely off of this guy’s script for making an LED strip light up for Super Hexagon.
My edit just strips out everything hexagon-specific and very very poorly tries to guess the right color for the LEDs based on the average color on 4 points in 3 sections of the screen. The outside edge, a spot that mostly falls in line with the rule of thirds, and 2 hardcoded random spots in the center that are placed so that they hopefully miss any crosshairs or other HUD info.
If you have multiple monitors it might flip out, consider modifying the section that picks coordinates so that they all land on the correct monitor.
Depending on what you have on screen it’s pretty well recommended to change the weights for each section down towards the bottom of the script. By default it’s heavily weighted to be colored the same as whatever’s in the center of the screen, which for first person games is usually where all the focus is. For movies or not-first person games you might want to try something else. For example for movies you might want to give the mid range more weight, since the mid range is placed roughly along with the rule of thirds, which for movies is where all the focus is.
After it picks a color, it’ll light up all LEDs on the first blinkstick with that color. In my case the LEDs are actually in my PC case which looks kind of neat. I’ve only tested it under linux, but it should work on Windows as long as all the requirements are met.