Blacks are milky grays when brightness is not at minimum value in all LED HMDs
Example: The sky in Dark city background of Go is washed gray when brightness is not 0.
It looks as simultaneous control of backlight + brightness, as legacy of OLED screens with no backlight.
Maybe to increase gamma could fix this common problem too.
This does not happens only in S and Go, also in Mixed reality LED and Index.
Maybe a better dynamic contrast could help too, or to change color space