Update 2 (09/04/2020 @ 05:46 AM ET): Apparently, the commands are still accessible on Android 11 Developer Preview 4 builds.
Update 1 (08/24/2020 @ 02:25 AM ET): OnePlus has silently patched the ability to truly access the color filter camera through ADB. Scroll to the bottom for more information. The article as published on July 17, 2020, is preserved below.
The OnePlus 8 Pro's color filter camera has been mired in a bubble of controversy ever since the phone launched. First, this auxiliary color filter camera was written off by many for largely being of no real use. Then, news emerged that the color filter camera with the Photochrom mode was capable of seeing through thin plastic objects and very thin clothing too! Consequently, the Photochrom mode was disabled in the next updates — first in China and then even on global variants (albeit accidentally for the latter). The device even went on sale in India with the Photochrom mode disabled out of the box! OnePlus then finally fixed the color filter's see-through issues with the OxygenOS 10.5.10 update by layering information from the sensor onto an image from the main sensor. But as it turns out, if you still really wish to use the auxiliary camera as it was originally set up, you actually can as the color filter camera is still accessible through a hidden app.
OnePlus 8 XDA Forums ||| OnePlus 8 Pro XDA Forums
XDA Member piskel found out that the color filter camera still remains accessible through the Factory Mode app on the latest update on the OnePlus 8 Pro. However, this app needs to be launched through ADB. Once the app is launched, you can keep it locked into the phone's memory to access it without ADB. The best part about this discovery is that you do not need to be rooted or even have your bootloader unlocked.
To use the Color Filter camera on the OnePlus 8 Pro, connect your phone to ADB and run the following the commands:
adb shell
am start -n com.oneplus.factorymode/.camera.manualtest.CameraManualTest
This will start the Factory Mode app. Once in the app, use the camera switcher icon in the bottom right corner to cycle through the different cameras. The color filter camera is positioned at number 4 within the app.
The question still remains of the camera's overall utility. The x-ray/see-through effect can be reproduced only on very thin plastics. The overall utility of the OnePlus 8 Pro's color filter camera mode is very narrow in scope, and you are much more likely to appreciate its novelty just a few times and then forget about it altogether.
[GUIDE] Access color-filter through command shell - XDA Thread
The images above are from Max Weinbach. I tried out the same on my OnePlus 8 Pro, and I could not locate any objects around me with a thin enough plastic shell to actually see-through. As far as clothing is concerned, the same results were observed. So the possibility of using this for nefarious purposes remains very, very limited, if at all.
Update: OnePlus has silently patched the OnePlus 8 Pro's color filter camera to no longer be accessible through ADB commands
Somewhere along the way, through intervening updates, OnePlus has silently patched the ability to access the OnePlus 8 Pro's color filter camera through ADB commands. You can no longer run the commands to access the color filter camera. The command no longer launches the factory app anymore and returns "Activity not started because the current activity is being kept for the user" instead. You now need to rely solely on OnePlus' implementation to get some use out of this hardware.
Source: /r/OnePlus
Update: Still works on Android 11 Developer Preview 4
According to XDA Senior Member cyberbandit1998, the ADB commands still work to surface the OnePlus 8 Pro's color filter camera, but only on the Android 11 Developer Preview 4-based build of OxygenOS 11 that was recently released. However, we do not expect the functionality to remain present on the stable builds when they do get released.