How to make my display Grayscale?

I found a way using an accessibility software. It isn't perfect, but this program: http://users.telenet.be/littlegems/MySoft/DesktopZoom/Index.html can be set to zoom 1000/1000 and has greyscale modes of 4,8,16,32,64,128,256 colors. It works on xp and Vista. Only issue is that occasionally, the color peeks through before the program greyscales it. The invert mode is very much like the high contrast theme.

Windows 10 go to:

Settings -> Personalisation

On the right hand side of windows, under 'Related Setting' -> High contrast settings -> Color Filters -> Chose a filter 'Grayscale'.

Short way:

Press Windows logo key+Ctrl+C to toggle the colour filter on or off.

If you have NVidia graphics, open NVidia control panel and set "Digital Vibrance" to 0% from here.

On my control panel for Nvidia Optimus so far I can't find any such setting. I can set Saturation to 0% for video content and that at least works for video playback (but not Flash content).