Hex colors are implemented on a basis of reasonable effort depending on whether the server supports Adventure.
Sponge and Velocity will always enable hex colors.
Paper 1.16.5 and later adds Adventure API support, which is used for hex colors in both chat messages and the disconnect screen. SpigotMC has a separate method for hex colors that is not supported.
The LibertyBans implementation on BungeeCord currently does not permit hex colors on the ban screen (even though this is possible), but it does in chat messages.
Improvements are possible on SpigotMC and BungeeCord.
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Description
Hex colors are implemented on a basis of reasonable effort depending on whether the server supports Adventure.
Improvements are possible on SpigotMC and BungeeCord.