If I were to summarize what 3D rendering is about, I'd say it's about trickery. While it's true it offers much more freedom to the creator to generate scene straight outta their imagination, it's also a very resources-hungry process - one that needs to be optimized for the creators to keep their sanity intact. So, to do that, we tend to cheat.
See, the only thing that matters is what the camera captures. As creators, our sole purpose is to make this look as good as possible. However, making a 3D scene look good often goes against the idea that only what the camera sees matters. The more items you bring in your scene to make it look better and feel more believable, the more resources heavy it becomes and the longer it will take to be finalized.
In this case, I use an HDRI (a 360 degree image) to offer Tracer and Mercy an environment to evolve in. Though, because the HDRI is only an image (no physical properties in the 3D space) it can be problematic when setting up lighting (lack of shadows). That's why in order to make light and shadows more believable on our protagonists, I had to build a small part of Anubis spawn through which sunlight goes through. But because the camera doesn't see that small replica of the environment, I didn't need to make it look good. So, it's grey.
All tricks.
While I've worked on optimizing "Resources Management VS How Good It Looks", this render still took 20+ hours to make from beginning to end - because no matter what, 3D rendering is a very long process!