As I've noted previously, I don't personally get the hype around 'dark mode' features. Aside from the health benefits (which can be significant), making the screen look different doesn't really do much for me, or at least, not as much as it seemingly does for others.
But many people do seem to get very excited about such - so without further ado...
Yes, Google is adding a new 'dark mode' option for Gmail, providing another way to protect users from the dangers of excessive blue light exposure, which can confuse your brain, and stop production of melatonin, potentially messing up your sleep cycle.
There has actually been a couple of ways to convert Gmail to dark mode for some time, but none of the existing workarounds have been complete, with gaps and issues in the process that made them hard to use (for example, while your Gmail screen might be in dark mode, any new email compose window would come up in normal, white screen, spiking into your retinas).
This new update is a complete dark mode option, which will no doubt be welcomed by many Gmail users.
The option is available in the latest version of Gmail on both iOS and Android - Google has provided specific instructions on how to activate Dark Mode for each device version here.