Galactic Night is an experimental nightmode app for rooted Samsung Galaxy S2, S3 and Note phones (don't bother trying on other devices) that lets you set various color modes on your phone for use in the dark, to save batteries, for astronomy, ebook reading in the dark (and during the day) and for other purposes. Currently supported special modes on many devices include: red, green, blue, no-blue, sepia, black and white, reverse and outdoor. E.g., in red mode, everything is rendered in shades of red. In reverse, all colors are reversed, which is nice for web browsing at night. In sepia, white is replaced with sepia.
Monochromatic color modes like red and especially green (because our eyes are very sensitive to green light, you can use lower intensities with green than with red or blue and still preserve visibility) can save batteries by using only one color of AMOLED subpixel. Moreover, except on some devices (e.g., the American version of the S3), these modes are designed to preserve maximum device usability: they don't just drop the other components of the colors, but use the overall luminosity of the pixel to set the red or green intensity, which means that even in red and green mode, blue things can still be used.
Because Galactic Night uses your Galaxy phone's mDNIe system, it should not significantly impact graphics speed.
WARNING: THIS IS EXPERIMENTAL SOFTWARE REQUIRING A ROOTED DEVICE. USE IS AT YOUR OWN RISK. In particular, there is a danger that that using modes like red, green, blue and no-blue regularly and for too long, especially at too high intensity, will result in burn-in on the AMOLED display, resulting in a color tint.
The black and white and mono sepia modes are useful for reading ebooks even in daytime with ebook reader apps (like the last version of the Kindle ebook that I tested) that incorrectly use subpixel rendering which results in colored fringes around letters in some orientation. The black and white and mono sepia modes fix this.
Unfortunately, the hardware on the US (or at least Sprint US) versions of the Note and S3 uses a different display controller from the international versions, and this display controller does not work for the black and white or mono sepia modes. I've also have not been able to get this working on 4.3 on the US Sprint S3.
1.10: Android 4.4 support
1.09: Restore settings after screen off on S2
1.06: Official Note 2 support
1.04: SGH-I727 support
1.03: SGH-T989 support
1.02: Improve screen-power-back-on handling on ICS; logo flash disabled by default
1.01: Support for US versions of the S3 and Note
1.00: official release