NegativeScreen is a Windows application allowing you to invert your screen colors. Apart from accessibility matters, this software is especially useful when you are surfing on the internet in a dark room, and the screen is dazzling you.
NegativeScreen was designed to work without impacting the performances and fluidity of your computer. Unlike the Windows Magnifier, which is also capable of such color inversion, it was specifically designed to be easy and convenient to use.
Different inversion modes are provided, including “smart” modes, allowing black and white inversion, while keeping colors (about) the same.
The different inversion modes listed might be of use to you, including smart inversion 3 ("overall desaturated, yellows and blues plain bad, actually relaxing and very usable"), negative sepia, negative grayscale, and especially grayscale.
[Looks like this was developed by yaurthek, so if it helps you, you know whom to thank.]