I actually read most books like this! Red text on black background. It's especially nice in the evening: light above 580 nm doesn't appreciably activate ipRGCs,

I actually read most books like this! Red text on black background. It's especially nice in the evening: light above 580 nm doesn't appreciably activate ipRGCs, so melatonin sythesis isn't inhibited. And if the device had an OLED screen, its battery can last for days. I wish GPUs had programmable scanout "hooks", so that you could run a bit of hard-realtime code to modify colors as they went out. As it stands, you can either twiddle the colorspace knobs (limited control, can't do perceptual color->grayscale), or you can get the system compositor to run a color conversion pixel shader to modify the display buffer. The latter is infinitely customizeable, but eats into frame budget, bandwidth, and runs the risk of not finishing in time for scanout. (Now I'm wondering if something like this has been added to more recent GPUs, or if it's been there all along and I didn't realize it. Time to do some research.)