With 8-Bit 4:2:0 in camera, what that means is that in-post you would have to add the darker underexposed look instead of having it in camera. With 8-bit 4:2:0 your camera is having a hard time reading color, so let it read color easier. Put the subject that is more in color in good amount of light. Make what's supposed to be in-camera, in front of the camera first in terms of a usable image, then dial the settings, not the other way around. To prove what I say even further notice how I at one point put a jar of jelly beans of many colors is in shadow and how much noise and how much of a hard time the camera is reading it in high ISOs, I then put the jar of jelly beans closer to a good amount of light and thus the camera read the colors easier and there was less noise on the jelly beans.