A new code commit in the Chromium codebase adds a new feature that will enable dark mode not just for the Chrome UI, but also content inside the browser window. This feature will likely come to Chrome Canary within the next few days, since it's already been picked up by Chromium's buildbot. Even so, it's not available in an off-the trunk Chromium build as of this writing on either Android or Linux. Looking at the log on the commit itself, it seems the buildbot has tried to add the feature multiple times, but it failed.
Obviously, there are some bugs to iron out. Since it hasn't been seen in action yet, it's hard to say exactly how the new feature would work. Since it will seemingly use a single flag across platforms, it's likely to tie into Chrome's underlying rendering engine, Blink. This would mean that, at some level, Chrome is going to call an inventory of the colors and light levels of a page, then figure out how best to darken that page on the fly.
This means that the results of the new feature will probably vary from page to page. This is to be expected, at first; the developers will have to hammer out bugs over time, and refine the feature so it works reliably across all sorts of pages. Behavior regarding all sorts of different content types will have to be defined, and decisions will have to be made as to contrast, aesthetic appeal, and usability.
Chrome isn't the first browser to get a dark mode. The biggest differentiating factor here is that Chrome is going to be handling dark mode at the render level with official changes from the developers, whereas most browsers, like Firefox, have a dark mode or night mode available as an extension. One notable exception here is the stock browser for Samsung devices, which offers a night mode that works pretty well right out of the box.
Chrome loyalists who don't want to wait for the new feature to hit can always simply invert all colors on the screen via an accessibility setting in Android. The problem with this is that images get inverted as well, and pages and other content that are already darkened to be easy on users' eyes and batteries will turn blindingly bright
This change will bring a comprehensive dark mode to Chrome users once and for all, complementing the system-wide dark mode seemingly coming to Android Q. Between those two things, blinding screens will seemingly be a thing of the past for those with Android Q devices.
One very fortunate side effect here, as mentioned above, will be battery life. A number of modern flagship smartphones, and even some laptops, have AMOLED screens. Pixels on an AMOLED screen are only activated if they're colored, meaning that you're not seeing a pixel display black – you're seeing it turned off. This means the more black you see on the screen, the less power you're using.
Blue light, a widely decried side-effect of our digital lifestyle that can mess with your sleep schedule, can also be severely reduced in this manner. There are already night modes in many apps and in Android that filter colors to reduce blue light, but a true dark mode with a predominantly black color scheme would do one better by simply turning most of those pixels off, at least on an AMOLED display.