How can I make the screen black and white?

On Ubuntu, some people have had luck doing this using Compiz Config Setting Manager. Run it and under Accessibility category, you'll find Color Filter and Opacity, Brightness and Saturation filters. There you'll be get the desired effect with the available options. You can try options related to Grayscale or decrease saturation to zero to get the black and white screen effect. (I can't tell you the exact option since my current distro doesn't have Compiz Config support).

Alternatively, you could do the same by adding the following lines in your Xorg configuration:

Section "Screen"
    Identifier "greyscale configuration"
    Defaultdepth 8
    SubSection "Display"
        Depth 8
        Visual "GrayScale"
    EndSubSection
EndSection

Reference answer.

Keep in mind that Xorg may not start with this configuration if your display drivers do not support such a low color depth value.

On my system (ThinkPad T61 Nvidia Quadro NVS 140M), when using proprietary Nvidia driver, to transform to greyscale I use following command:

nvidia-settings -a [DPY:LVDS-0]/DigitalVibrance=-1024

To return to color I use:

nvidia-settings -a [DPY:LVDS-0]/DigitalVibrance=0

I assigned this instructions to key combinations, so I can change my display to grayscale and color more easly.

I hope this will be some kind of inspiration to someone.