I've enabled the use of Minecraft's text formatting codes in chat, all the codes except 'Obfuscated' are now available to all ranks.
A full list of the colour and formatting codes can be found here:
http://www.minecraftwiki.net/wiki/Formatting_codes
When using them in chat you need to replace the character before the letter or number with an '&' symbol, for example:
&4Hello! - would make the text appear red (as '4' is the code for the colour red).
&lHello! - would make the text appear bold (as 'l' is the code for bold formatting).
&4&lHello! - would make the text appear red and bold (a combination of the other examples).
The codes can be combined in just about any way you want!
Also please note that you can also use any of the colour codes on Lockette signs, however Lockette signs will not recognise the other formatting codes such as bold or italic.