Do I have to memorize a color code when facing a different faction or does red = bad?

As the old saying goes, If it's red it's dead

Thats how I want it but the BloodAngels,Evilsunz,Wordbearers and Saim hann are red so there might be more accidental friendly fire for those wearing red.

I'm kind of hoping that there isn't color coding so we really have to look where we're shooting.

I think it's going to be pretty obvious to see who is your enemy, lol.

There's no need to try and colour code them, it's really obvious when you look at an Ork or an Eldar or a Chaos Space Marine (except the CSM warbands who disguise as loyalists) and realize they are your enemy if you play Space Marine, and the same for all factions.

If you can't tell who your opponent is just by looking at them from a distance, you might want to look at the models from table-top and dawn of war again, there is no difficulty figuring that out.

There's probably going to be a red targeting reticle over the nearest enemies in your vicinity or wherever you have zoomed in to to signify that they indeed are not friendly and the bullets they're flinging your way might hurt.

I like the PS2 approach. You can choose whether to use a universal "red is bad" scheme or use the actual team colors. The tricky part here would be in making sure similar colors are distinct from one another. The difference between Mephiston Red and Evil Sunz Scarlet isn't very obvious to most people.

Outside of a minimap (do we even have one?), there's not much need to color-code enemies. Aside from possibly SM vs CSM, telling friend from foe will be pretty easy.

If you look at something and it has a red health bar over its head then for the love of the All-Father and Russ shoot it with your Bolter if that fails use your Bolt Pistol if that fails use your blade or Chainsword if that breaks use your fists if your arms are broken then kick the enemy to death if your legs break rip their fething throat with your fangs.

TF2 does something like this. If you look directly at an ally, it displays their name with your team color (either red or blue), but it displays nothing when looking at enemies. That would be plenty sufficient. The color of their name is unimportant but could probably be accompanied by a faction/subfaction logo.