: I just got another theory: The red text probably appears as black to them,
: but the black terminal screen may actually be an infrared or UV color that
: appears black to us.
That's a very good idea. UV can be partially seen by humans in the form of blacklight fluorescence (a neon bluish purple) like in bowling alleys and hospital bathrooms, but a lot of the actual radiation is as invisible as we think. Plus if the terminals were blacklit, maybe the translator filters out the UV as it would appear weird and feel odd to read. (also because I doubt Bungie could easily depict the tiny part of UV we can see in a machine that relies on the visible spectrum only)
While we're on the topic, some people can see more real UV than most, but only if they have artificial lenses. Since Marcus is a battleroid, there's no reason why he couldn't see ultraviolet other than the above bit about it being hard to depict correctly.
https://www.newscientist.com/lastword/mg24432591-000-super-seers-why-some-people-can-see-ultraviolet-light/