GregAtkinson Thanks for the suggestion of light bulbs! I'll have to try those.
When detecting differences in the flicker of different color subpixels, for Nightshift, I measured the flicker of the different subpixels (using the microscope and slow-motion video) on a completely white (or sometimes gray) screen without Nightshift and then using the same white (or gray) screen, but with Nightshift turned on at its warmest. It's super labor-intensive to do this using the Photoshop histogram/luminosity function, but I was glad I did. Before doing this test, I could feel that Nightshift was doing something that badly hurt me, but before this test, I didn't have good evidence for why. It's dramatic how much more the green and especially blue subpixels are fligckering than the red supixels during Nightshift.
I could also detect differences in the flicker of different color subpixels (without Nightshift) using other colors on the screen. To find dramatic examples to measure with the microscope (since microscope/video measurement Photoshop analysis so labor intensive and triggering of symptoms for me), first I measured flicker with a flicker meter of different colors when only a single R, G, or B value was nonzero, at many settings. Then I chose to make 2 of the R, G, or B values nonzero, choosing combinations of values that on their own gave different flicker meter readings. Then when I recorded slow-motion microscope videos, i could see and quantify differences in luminosity of differently colored subpixels as they flickered. I could also put camera color filters between the flicker meter and the screen to get readings for different colors (Tiffen Red25, Blue47, and Green58 filters were the most useful for me). However, the microscope slow-motion video measurements tended to show color-to-color flicker best because I could measure individual subpixels and didn't have the interference between differently-phased flicker patterns that obscures readings with the flicker meter. Different screens had different colors with the most dramatic color-to-color flicker. On the screen I use most, i can mostly limit the colors that are used. I immediately feel pain/pressure in my head if I have even a small part of the screen displaying something with high color-to-color flicker.
I'll be interested to hear what you find out with your method!