I'm not sure exactly what this means. Camera and film/source as usually always neutral except for white balance, and I guess film stock, but what do you mean not in post? When where you doing it before and when are you doing it now? Perhaps that's the best way to ask it.
This wouldn't technically be called a colorist process, I just call it that because it's used to replace that process. What's responsible for the confusion is that in UE5 we were doing the standard colorist process, but it was encoded into the camera itself, standardizing stylistic templates and making them portable. In this new way, I detatched the color profile from the cameras, leaving them nuetral, and instead instituted master controls that affect physically based shaders in the environment through a selective hierarchy in a meta node. So imagine just installing a few extra dimmer knobs in your room, but instead of affecting light intensity, one of the knobs changed the underlying HSL of the paper material used as a base for any wallpaper design, etc. Then you make that set of dimmers universal, so it can be plug and play across different shooting environments.
So I can take this node graph blueprint and port it over the to canyon set, and just have one master control for the rock material. Purple or gold canyon in 3 seconds with accurate light bounces. So basically, the trick was to install a color control hierarchy that affected physical materials, rather than the textures on top of them.