Also, as was pointed out in another thread, packet color at night is basically impossible to see. We don't expect people to pay attention to what color packet they are hit with. We expect them to notice they've been hit and respond to the call - or to get a clarify on what it was if they don't know.
I think
@Tantarus and
@Draven had a point about it being useful for visually sizing up an enemy, especially with regard to alchemy. (Spell vs bow tends to be obvious based on if they are carrying a bow/xbow or not; but noticing alchemy packets seems especially relevant to those with poison defenses.)
With that said, it feels like a rule that is adding mild OOG logistical complexity (tracking packet colors) for something that has inconsistent mechanical results. (IE, being hit by a blue packet doesn't actually tell you anything about how you resist its effect -- the only way you can know that is by hearing the call.) I think removing packet color restrictions mildly simplifies the rules, and avoids accidental confusion of people thinking they can avoid an effect because is wrong assumptions about what a blue packet means. The last thing I want is someone trying to adjudicate or argue a miscast because of a disagreement on packet color.
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Thinking more, I do find the sizing-up-the-alchemist example pretty compelling. Maybe only Alchemy should have a restricted color? Arrows already have a solid indicator in that they require a bow.
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Or I suppose taking this the other direction, should we be thinking about if we should be doing more with colors? Should earth vs celestial result in different color packets? It'd let you size up and know if you are coming up against someone with Doom or Prison. And it might result in interesting dynamics like some enemies focusing on healers because they could tell who they are. (You could also arguably do something interesting around necromancy use and packet color...) And we are already expecting people to juggle 3 different color packets - so there isn't really a complexity argument against this.
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I think my _*personal*_ preference would be to either eliminate packet color except that only alchemy is color coded. A very small part of this is because I'd like to have arrow packets that color coordinate with my outfit, but its mostly because I think adding rules around packet color (with the exception of alchemy) doesn't really add anything other than complexity. And much like requiring magic swords to be white, its something that could use to be relegated to the rules history.