[Simon Logic]

I think SHOW_COLOR is redundant because you can freely put color codes (so, worth to make contants like %green, %red, %blue etc) into format string. But you need a new cvar which defines default color also.

PS. Is it properly to define cvars within plugin_precache() ?

PSS. LAN ip is 10.0.0.0/8 & 172.[16-31].0.0/16 also.

PSSS. Also you forgot to handle "127.0.0.1" ip (compare with "127." is enough) because when you're connecting to dedicated server from the same ip you get "127.0.0.1" ip instead of "loopback" (at least on win32 platform)