Use the home button triple-click trick for night reading.

http://lifehacker.com/5957534/invert-your-phones-colors-for-...

Another thing that really helps is f.lux for iphone:

http://justgetflux.com/ios.html

But this sadly requires jailbreaking.

Thanks, I do remember that. There is the problem though of those apps which use a dark theme, that therefore become light upon negative view. Hence, why I'd prefer a single theme enforced.

Themes don't work; Windows Phone has two choices and a lot of developers simply support only of them.

Yes and No :-)

Most utility apps that aren't supporting an existing brand will often support both themes. However I've noticed that apps that are already branded will go along with only the theme that works best with their brand.

The way themes have worked historically is that the application isn't consulted.