I don't know if this can be done in vBullitin, but what about a dark theme? This would be a good thing for me, since the white is just too bright for me when I'm on my phone, even with the screen brightness on its Lowest setting (sorry if this is in the wrong section btw, didn't know where else I should post this.)
Most phones will still light the backlight when displaying black, you get quite a bit of light emitted. The slight blue hue emitted by a phones backlight (even when they are trying to display "black") is rather harsh on sensitive eyes (as the human eye is more susceptible to glare from blue than any other colour, also the main reason why some people are fooled into thinking their 6000k light source is brighter than their 4300k when its not, they simply see more glare from the additional blue hue). It also stimulates the body into producing a particular hormone which aids in synchronising the human body clock and fools the body into thinking it is daylight during the darker hours. Reducing a displays colour temperature introduces a red shift. Accurate colour reproduction is impeded, however the red light is perceived less harshly (actually the reason why emergency lighting tends to be red) and the body clock will not align to it. Twilight on android claims to alter colour temperature, really it just adds a slight red filter and adds far improved brightness control rather than truly altering the display settings, but end result is the same. f.lux will truly alter colour temperature settings under windows and OSX and also offers an iOS version that I presume is more akin to twilight (as I dont think iOS apps can actually interfere with GPU and display settings properly). Both allow automatic changing between a filtered and non filtered mode, f.lux actually lets you set what location you are at and will calculate when sundown is and automatically switch to the lower temperature when the sun lowers and switch back when the sun rises, twilight is time based i think. I'm pretty sure NVidia and AMD control panels have a colour temperature setting, think the intel one does too. That would be more permanent rather than the time based solution in f.lux, but is with the full support of your display driver rather than cruder hacks. There is also a setting for it in windows phone but its the same as NVidia/AMD control panels in being an actual set and forget type setting. Worth a shot for all websites.
Many mobile web browsers (including the stock android browser) can invert the colours for you, so the white background would become black and the black text would become white. This may be useful although it will mess with any images people post. There are also add ons available for mobile firefox that allow you to change the background colours as you wish: https://addons.mozilla.org/en-US/android/addon/black-background-white-text/?src=search With that add on i managed to get better result by changing its settings from "Default" to "JS mutation observer", It even did a pretty good job of the header. If your phone has an OLED (SAMOLED in my case) screen like mine you can even enjoy the battery life savings from doing this.