This feature is now in (we moved to github over the last few hours, so go here: 
https://github.com/EQEmu/Server/commits/master for the latest source).
The syntax is:
	Code:
	quest::gmsay(<messsage>, [color], [toworld], [guildid], [minstatus])
 So to send a yellow message to the guild of the player:
	Code:
	quest::gmsay("The earth shakes and a huge hill giant appears", 15, 1, $client->GuildID(), 0);
Parameter 2,  15 = yellow
Parameter 3,   1 = send to all zones
Parameter 5,   0 = required admin status to receive the message