Bukkit

Supported colours are any that exist in Bukkit's ChatColor interface. They are as follows:

• Black: &0
• Dark blue: &1
• Dark green: &2
• Dark aqua: &3
• Dark red: &4
• Dark purple: &5
• Gold: &6
• Gray: &7
• Dark gray: &8
• Blue: &9
• Green: &a
• Aqua: &b
• Red: &c
• Light purple: &d
• Yellow: &e
• White: &f
• Magic: &k
• Bold: &l
• Strikethrough: &m
• Underline: &n
• Italic: &o
• Reset: &r

So, to make the text on a line blue then red you would type: /signedit <line> &9Blue &4Red!