Turns out, there was a little more to the OxygenOS 10.5.10 update for the 8 Pro than we thought. Although it isn't mentioned in the changelog, we can confirm that the update also re-enables the "X-Ray" color filter infrared camera on the 8 Pro, previously disabled in the 10.5.9 update before it was pulled.
Above: The "Photochrom" mode is back. Below: And it works.
The full (and rather chunky) changelog for the original release did note quite a few camera-related changes when it started rolling out last week, but it omitted the fact that the color filter had been re-enabled. We didn't know the functionality was back until the update started rolling out in the US. As you can see from our testing above, the "Photochrom" camera mode is back and seems to work almost precisely as it did before.
OnePlus said that it was only disabling the color filter camera in China while it worked on an as-yet-undefined fix for the camera — which is alleged to be able to see through some visually non-transparent materials like certain plastics and thin fabric. However, an update was "inadvertently" rolled out, which disabled the camera in all markets.
If you were among those that ended up installing OxygenOS 10.5.9, this latest 10.5.10 update should re-enable the color filter camera, in addition to delivering other features like H.265 video recordings support, May 2020 security patches, and other fixes.