I like use flare as a symbols:
white: I'm just passing by. I will not attack you.
red: come closer and I will attack you
BLUE: let's trade!
Community Weekend starts on June 15th!
Good news! There's already effectively a blue flare; The Lost Seafarer firework! It's a common, single firework that drops a small blue flame that drifts down slowly. It's not as bright as a standard flare, but if you're close enough to ask for trades, that could suffice.
Now it's just a matter of usage to establish meaning.
@baybaton15975 I think one issue is that people don't tend to trade. The closest you'll get is a alliance.
Even with a set of meanings it doesn't necessarily mean they'll be used for the intended purposes a 'tools, not rules' kinda thing.
There has been many attempts to make some form of non-verbal communication in this game. Those range from trying to make flags mean a certain thing, like white means friendly. However, nothing ever sticks. The same problems arise that nothing gains enough traction, and even if something did, players use those newly created tools to just bait people into getting attacked.
Not to just put a damper on things, but realistically this won't go anywhere.