If you wish to use other colors, not just warcraft standard ones, use
this - great tool by Pyritie, or
this - great warcfta3 model editing tool. After instaling, look for 'Extras' on task bar, choose whatever color you want and click 'Generate'
You need to know just two important things about color string, already mentioned above by @Saif.
Color string starts with '|' then there is a code of given color, and ends with '|r.
So basically when you see: |c00ff0000|r your eyes should see: |c00ff0000 and |r.
Gama interface - To find it, open your map, on taskbar there is Advanced field. From that direction head to Game inferface, and find 'Text' fields. There are all the messages displayed by game.