OK, first of all I don't know which games this works in, as I have only tried in in css, it might work in other source and source2 games, but I don't know.
Now then, you all know how to make your name show up as 'unconnected' by typing setinfo name "" in console before joining a server, yes?
Once your in a server, with the name unconnected, you can change your name by typing "name urnamehere" once you've done that, your still unconnected and show up as a blank space in the admin lists, and you still don't show up in player list.
Now, the fun part. Lets say you make your name "Owned By Myg0t", if you type "name "Owned By Myg0t"" in console, and make your name that, then when you type "Owned By Myg0t", or whatever your name is in chat, as long as its the EXACT same thing as your name, it will show up in color, red if your a t, and light blue if your a ct.
A Couple Notes:This does not work when your dead. If the server changes maps, or you change servers, your name will not be unconnected anymore, and it will just be "Owned By Myg0t", and it will not show up in color. This is mostly because when people see you typing in color, they freak out and think your hacking the server or them or something, because 99% of people who play css, have never seen someone type in color before.
http://sfi72.com/Images/Color1.jpg
http://sfi72.com/Images/Color2.jpg