OpenRGB

Installation

add to /etc/nixos/configuration.nix:

services.hardware.openrgb.enable = true;

No need to add OpenRGB to systemPackages.

Turn off RGB

If you'd like to turn off all RGB devices supported by OpenRGB, consider something like:

{ pkgs, lib, ... }:
let
  no-rgb = pkgs.writeScriptBin "no-rgb" ''
    #!/bin/sh
    NUM_DEVICES=$(${pkgs.openrgb}/bin/openrgb --noautoconnect --list-devices | grep -E '^[0-9]+: ' | wc -l)

    for i in $(seq 0 $(($NUM_DEVICES - 1))); do
      ${pkgs.openrgb}/bin/openrgb --noautoconnect --device $i --mode static --color 000000
    done
  '';
in {
  config = {
    services.udev.packages = [ pkgs.openrgb ];
    boot.kernelModules = [ "i2c-dev" ];
    hardware.i2c.enable = true;

    systemd.services.no-rgb = {
      description = "no-rgb";
      serviceConfig = {
        ExecStart = "${no-rgb}/bin/no-rgb";
        Type = "oneshot";
      };
      wantedBy = [ "multi-user.target" ];
    };
  };
}