I'm afraid that Darkvision doesn't give colours under the D&D 5e rules and I guess they are on a Darkvision YES/NO switch which stays on no matter what the external lighting.
There is an argument that, in a primarily visual medium like a CRPG, that part of the rules/lore could be dropped for a more colourful experience, but I like that the Darkvision spectrum is Darkvision and not just somebody turning up the lights.
As for what I see as your actual point (about Darkvision not being normal vision when others have torches), yes, I agree. It might have been overlooked by the developers and could count as a bug.
Yes I know it doesn't give colour - which is why I'd like the areas in shadow to be visible, but just in shades of grey & for actual light be in the proper colours.
My comment on superior darkvision is that you'd probably get a bit more of the colour fading before it goes greyscale for a further distance.
