Windows 10 has global colour filters that make this super easy. Windows key + Ctrl + C toggles it on and off, and you can change which filter to use in Settings

Windows 10 has global colour filters that make this super easy. Windows key + Ctrl + C toggles it on and off, and you can change which filter to use in Settings → Ease of Access → Colour Filters. In addition to greyscale, there are colourblindness filters for red-green (green weak), red-green (red weak), and blue-yellow.