Not with lightning speed and it doesn't mean you are 100% guaranteed to be recognized. You can tell
your pals the name of the person who killed you, or post a screenshot, and this better reflects "spread
of rumors", not putting people on color list, which not only always works perfectly, there is no way that
anyone can forget about you (actually they don't even have to ever heard about you), but also it works
for all characters you have, which makes no sense either in some cases.
Don't pin in realism, you said it yourself. Color can indicate threat, belonging to a certain player group, i think it's irrelevant how fast the color spread, players still don't know the exact player or what they done if they copy paste a list and it's up to them what they make out of it, if someone see appropriate to pull the trigger instantly it's his choice, someone else might start a conversation and it might just turn out it's a misunderstanding he has been tagged as an outlaw in some list of players.
It's a good thing when the list works for all characters, why? Well there is this thing no matter with how much alts you play, you still are the same person, means that by your logic it wouldn't make sense that you remember someone shooting you while you are on a different character. It's not like you loose your own memory by playing a different character(shouldn't loose the color in that case), it's just keeping track of them by color, you might be a PK with one alt and APK with another, colors are the same, but you can act differently and the same colors might mean something completely different and associate with something else for the player who plays with the same list.
Don't pin realism, game doesn't supposed to make sense entirely.
It would make sense if faction allies (specified in terminal as whole factions) or faction friends (individual
people) were colorized green for all faction members and that's all that is needed IMO. And make sure
followers don't attack them if set up properly (not sure how it works now). So you won't have to make
new factions just to make some alliances.
That is not different from old NC, you set some player group in a terminal and suddenly countless players you don't know, haven't talked with etc. etc. instantly become friendly(in lightning speed by writing one sentence in some terminal) and all your alts are familiar with your friends faction by color?
It's the other side of the same coin.
Don't try to re-invent a wheel.
And I think what would be good would be an option to colorize your killer if your character could see who
killed you and the name isn't colorized yet.
I think it would be a good option to just bring back old NC.