Very few developers give a shit about accessibility. It's still largely a joke. I run Windows 8 and use High Contrast themes, but so many apps still don't comply with the HC colour schemes.
Applications often have hard coded font colours/sizes - so you end up with black on black text (oh my goth!) or apps that don't render properly with a non-standard DPI.
Microsoft still insists on locking down Windows so that you need to resort to replacing system files to enable custom themes.
The web is horrible in High Contrast mode using IE or Firefox.
Linux is better in some regards but there are still apps that have hard coded font colours, I haven't used a Linux desktop in a while (I use Debian and just ssh for my needs) but last time I used Gnome/KDE and others there were still issues.
Google Chrome is the worst, there are addons like Hackervision etc but they slow down the browser and are not a perfect solution, better than nothing and a huge help for a lot of people but it's still lacking.
And on mobile phones/tablets: To have white on black text in apps I have to root my phone, install a custom rom (I use SlimROM) and I have to resort to third party sources for modified APKs that have white on black text. Which is obviously a security risk.
Yes you can invert the entire screen on Android, iOS but that inverts *everything* and that also means that if you have a black keyboard, then your keyboard becomes white, or that page you're looking at has various bright/dark areas that, well, just invert to the opposite. It makes so much more sense to let users choose their desired text colour, background colour and other things and use those.
It's even worse when companies don't give a shit about their users, I've emailed many developers/companies asking politely to follow the Windows colour scheme, some have been helpful but the majority don't respond or care.
It's outrageous that in 2015 it's easier to overclock adn watercool my CPU than it is to change the UI colours/fonts on my computer.
Microsoft has made improvements, Windows 8 now lets you have a high contrast theme AND fullscreen magnification (like good ol' Compiz did) and I've written a bit of Autohotkey script to improve it but it's still lacking, you can't change many elements of the High Contrast theme, if you want the window borders to be non-white, you have to change the Button Text colour value (or it's something else non-related to window borders)
Another issue (for me) is that low vision options for phones is always a case of: Normal users get the cool themes/GUI but low vision means you get the unchangable theme, why not just let us set the colours/layouts/styles *WE* want and work with that? ie: Windows 8's high contrast theme is very useful and a big improvement but because I can't tweak it much, I am forced to have white lines (window borders/outlines of things) everywhere, which is NOT eye-friendly if you have retina problems or suffer from migraines (lots of outlines/grids = migraine attack)
So if anyone reads my comment and is a developer, please run your OS in a High Contrast theme, see how various apps don't comply, see how much of a fuckup it is trying to surf the web with a high contrast theme and try improve your code to comply and encourage your friends to do the same.
It's also not just us low vision chaps that hate white UIs, so many of the users I assist at work ask me how to change the colours/fonts to make it clearer/less bright/comfortable because staring at a PC/phone/tablet all day is NOT comfortable for many.
(please excuse brevity, software accessibility issues gets my blood boiling) :)