Running latest Spigot, but i have latest plugin PermissionEx, Vault, EssentialsX, EssentialsXChat.
I'ved try this formatting codes but not working.

List of working:

• &1 to &9
• &e
• &a
• &b
• &f

Not working:

• &l
• &n
• &o
• &k but turns to Bold
• &m
• &r

This is would be nice if you fixed this

Please paste your entire config.yml.

http://pastebin.com/Edmn35zN

I have the Donators ranks and i'ved setup to pex then, the prefix is &f[&a&k::&4&lDonator&a&k::&f]
The &k format turns to bold and it won't magic

This is an extremely late answer, so I don't know if this is useful to you anymore, but there is a chat format permission which you must set for those to work properly. Config does not affect it.