Why is it that in most Operating Systems the "Inverted Colors" display setting is considered an accessibility feature? Both Windows and OS X include this option so it seems to be a recognized feature and not not a vendor specific quirk.
I understand that some users are color-blind. This could possibly justify the Black & White, or grey-scale modes for developers wanting to be assured that the experience is cohesive for everyone. What I don't understand is how or why does inverting the display color help someone with any specific, visual impairment or dysfunction.
As a programmer that wants to understand the need so that I can develop better, accessible software, what purpose does this feature serve to the end user who has some form of visual impairment?
UPDATE
I asked this question quite a while ago, however, it just dawned on me-- I think I am one of those individuals that this feature was designed for. I almost always try to keep the contrast reversed from the typical settings for my text displays. I hate white backgrounds with dark text! As a coder, all of my textual GUIs are black with green text. This isn't just a throwback to the old monochrome, green screen days. The pairing of the two colors is quite comfortable to my eyes. However, stairing at to much black-on-white actually hurts my eyes from some form of eye strain.
I mention this in an update because the color inversion feature is not useful.. it's annoying! As someone who needs a good feature like this, it's a shame that all implementations that I have ever seen are just a poor attempt at solving a problem. I would hope that Apple, Microsoft and others have done their research but I'm guessing that might not be the case. Color inversion just feels like slapping a band-aid on a bigger problem.
Developers, if you want to help people who need such a feature as to prevent eye-strain, find ways to change the text and page background and not necessarily the entire display.
Answer
Research generally suggests light on dark is harder to read in most cases but considering we're talking accessibility, you should know that results for those with normal vision don't necessarily hold true for those with various vision impairments.
I've heard higher contrast (the mode in Windows is called High Contrast mode I think) can be easier to read for those with impaired vision though; the white text seems to stand out more. I'm curious as to why that is psychologically; the actual contrast ratio should technically be the same between white on black vs black on white.
Note that it's recommended to increase font sizes and leading when inverting text colors:
When reversing colour out, eg white text on black, make sure you increase the leading, tracking and decrease your font-weight. This applies to all widths of Measure. White text on a black background is a higher contrast to the opposite, so the letterforms need to be wider apart, lighter in weight and have more space between the lines.
Also, a common reason for white on black (which this feature mostly produces) is for night reading; many e-readers offer a Night Mode with white on black. The black screen is less painful to read with low to no external light.
Another reason it might be common is simply because it's easy and relatively safe to to implement. Compare it to other obvious color effect options; if you tried to Sepia tone the whole screen (an effect I've seen to make reading easier on the eyes) you would reduce contrast significantly. Turning things black and white could eliminate color cues used to differentiate interface elements.
Simply inverting colors preserves the relative contrast between UI elements (so you won't have black text on grey backgrounds), so it's a "safe" effect at the least. And if it doesn't help, no harm done, just undo the effect.
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