Switch screen to greyscale temporarily

Question

I am working on graphics design which shall be used in presentations (Powerpoint, color) and web (color) but also be suitable for printing (greyscale).

Since I work in the programs defined by the customer (e.g. Powerpoint), there's not always an option to turn things to greyscale to see what it looks like. Even if there would be such an option, it usually needs several mouse clicks and an undo operation.

The tool I am looking for

• turns the whole screen to greyscale
• must support multiple monitors (it's not sufficient to turn only primary screen to grey)
• is independent of the target application I'm working with (e.g. also works with Notepad)
• allows continuing working in the target application (e.g. does not rely on undo functionality)
• allows custom definition of a shortcut for turing the feature on and off, preferably the same key for toggling
• has a reasonable tool price (less than $15, gratis preferred)
• works on Windows (Win7, but would be nice if Win XP is supported)
• is independend of the graphics driver (I know that some graphic drivers support that out-of-the box)

Answer 1

Finally I found NegativeScreen

✓ turns the whole screen to greyscale
✓ supports multiple monitors
✓ is independent of the target application
✓ allows continuing working in the target application
✓ allows custom definition of shortcut
✓ is free (GPL license)
✓ works on Windows 7
✗ works on Windows XP
✓ is independend of the graphics driver

I created the following greyscale matrices:

Grayscale weighted=win+alt+W
{ 0.3,  0.3,  0.3,  0.0,  0.0 }
{ 0.6,  0.6,  0.6,  0.0,  0.0 }
{ 0.1,  0.1,  0.1,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  1.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  1.0 }

Grayscale from red=win+alt+R
{ 1.0,  1.0,  1.0,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  1.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  1.0 }

Grayscale from green=win+alt+G
{ 0.0,  0.0,  0.0,  0.0,  0.0 }
{ 1.0,  1.0,  1.0,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  1.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  1.0 }

Grayscale from blue=win+alt+B
{ 0.0,  0.0,  0.0,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  0.0 }
{ 1.0,  1.0,  1.0,  0.0,  0.0 }
{ 0.0,  0.0,  0.0,  1.0,  0.0 }
{ 0.0,  0.0,  0.0,  0.0,  1.0 }