If i understand you correctly i do this with mumble (Found here on WoWI)
in the config.lua file
Code:
CHAT_WHISPER_GET = "From %s:",
CHAT_WHISPER_INFORM_GET = "To %s:";
you may change the colors.
for example:
Code:
CHAT_WHISPER_GET = "|cffff0000From|r %s:",
CHAT_WHISPER_INFORM_GET = "|cffff0000To|r %s:";
Tho, mumble does change the entire ChatFrame so I'm not sure if you would want that