Please don't. Pure-white pages are painful to look at, let alone try to read -- just because our monitors can go all the way to #fff doesn't mean that's a good color to use more than once in a (rare) while.
Laptops tend to have the ability to conveniently adjust brightness, but then everyone went with ambient light sensors, and because they’re really pretty terrible at getting it right, laptop and OS manufacturers opted for erring on the side of excessive brightness, and so laptop screens are normally somewhere between too bright and way too bright.
Desktop screens tend to be hard to adjust the brightness of, because the physical unit’s OSD approach to changing brightness is awful, and OS vendors haven’t hooked anything helpful into it for reasons that quite escape me. So most people still have their screens set at the default brightness level, which is way too bright for anything but direct sunlight.
I remember with fondness CRTs that had a physical brightness dial that you could turn. So much better than what we have now.
Phone screens… yeah, they’re normally too bright too for similar reasons to laptops. Again I criticise ambient light sensors.
I went to quite some length to get the screen brightnesses for my Windows laptop and the external displays I normally use even vaguely sane, involving obscure freeware from ten years ago and deep diving into Windows APIs; there are basically two different APIs for working with display brightnesses: laptops’ internal displays use one, and external displays use the other (the internal display is also available through the other, but it doesn’t actually work for changing brightness). Said other API which external monitors need is exposed absolutely nowhere in any UI at all. (Windows basically lies about being unable to adjust brightness of external displays in its Settings app.) Screen-brightness-adjusting keys don’t seem to be interceptable (no hooking onto XF86MonBrightnessUp and XF86MonBrightnessDown as I did on my previous, Arch Linux, laptop), so your only recourse for linking the external displays’ brightness would be detecting the internal monitor’s brightness changing and effecting. (Incidentally, the jump from 0% brightness to 10% brightness is consistently massive on LCDs; I worked around this on Linux by making a logarithmic scale wrapper around xbacklight, but I can’t fix that conveniently on this laptop.)
At present, I just type “b 0”, “b 40” or whatever into Command Prompt and it invokes a CLI-based external-screen-brightness-adjusting program.
In my home office, my external displays normally operate at 20–40% brightness during the day, though I’ve gone up to 70% on occasion before, and 0% brightness during the evening (and I’d prefer −20–−10%; most screens’ minimum brightness is unreasonably bright).
It’s not anyone’s job as a web designer to insist they're wrong.
I will continue to recommend that people reduce their brightness in almost all cases. That’s my job as a friendly person.
As a web developer, though, there is little scope for insisting that they’re wrong, which is why I say we have to take most people’s badly configured monitors into account.
But this goes both ways. I've seen developers complain about the W3C accessibility standards on contrast because it looks too severe on their retina display full-brightness Macbook.
But the relative cost of having too much contrast (it's uncomfortable to read, but still perfectly legible) and the relative ease of fixing it (turn down your laptop brightness) is very minor when compared against the many people with crappy, low-light displays that can't adjust their brightness or fix the problem of low contrast text.
Often what people mean when they say to optimize for what people have is that they'd prefer to optimize for the highest quality devices first. But for a nontrivial number of websites and demographics, those devices are the minority, and in those situations high-contrast black-on-white text will look better on a wider variety of the devices that ordinary people are using.
If high contrast is painful to look at, and you can't control web designers throughout the world, but you can control your own web browser... then why are you still suffering?
Just off-black on a slightly creamy white.
May even stick with #000 for text.
Giving users ability to select a white, off-white, inverse, or solarised scheme is also useful.
See also https://contrastrebellion.com
My variant: