The greyscale mode is one of the features that nobody thought they'd need but want it now anyway. Essentially, it involves rendering your display a dull shade of black and white, reminiscent of the movies of yesteryear. Now, why one would actively pay for an OLED panel capable of displaying millions of colours and set it to display only two, is beyond me, but, to be honest, it does give my Pixel 2 XL a rustic, old-fashioned feel which is beginning to grow on me. Here's how you can enable it on your Pixel 2 and 2 XL.
STEP 1: Enable Developer Options
Unfortunately, the greyscale mode, for now, is hidden deep within the developer options, which isn't accessible until you manually enable it. For that, you need to head over to your phone settings and select the option that says "System", as shown below:
Once inside, select the option that says "About Phone". Developer options are already available to me as I've enabled it earlier.
At the very bottom, you'll see a tile that says "Build Number". Tap on that repeatedly till the device confirms that developer options are enabled. You will be asked to input your PIN/Pattern after this step.
Once successful, enter the developer options from the menu shown in the second image.
STEP 2: Open Developer Options
There'll be a ton of advanced settings in the menu, so you’re going to have to do a bit of scrolling to find the one you want. Scroll down to the “Hardware accelerated rendering” section and find “Simulate colour space”. Tap that, and choose “Monochromacy”.
Step 3: Relive The Magic of The 50s On Your Phone
And that's it. Your Pixel is now in black and white mode. The setting will persist across reboots and updates, so to get your display back to its original state, you will have to navigate back to the same location and disable it.
We don't recommend playing around with the developer options too much, as there are are some legitimate phone-breaking options in there. You can, however, tinker around with the colour space to adjust the colour temperature of the panel to your liking. It is enabled on all devices running Android Oreo 8.1, so Pixel, Pixel XL and Nexus users can also make the changes, if they so desire.