Perhaps you don't wander into the Android accessibility settings very much, but some users will be very happy to see what's going on in this menu as of the L release. Literally, they will be happy to see it. Android L has support for color inversion and correction for color blindness.

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These new options are under the Display section in Accessibility. Color inversion does what you'd expect – it inverts all the colors for a super-contrasty look. Color space correction gives you the choice between six different types of color seeing deficiencies including dichromacy and anomalous trichromacy varieties. Both color inversion and color space correction have toggles to activate from the settings, but you can also have a toggle placed in the Quick Settings panel for color inversion.

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Screenshots don't pick up these screen changes, so there are some photos above showing (left to right) the regular screen, inverted, deuteranomaly (red-green) color correction, and tritanomaly (blue-yellow) color correction.