I don't mind colours when they're not abused (I DO consider a multicoloured <><><> on each side of the message abuse.)
Even just auto colouring messages is abusing colours a little bit because you could change the local options (Alt+K) instead of making someone who has a <insert colour> background either strip colours (losing a feature that's handy when used properly) or change his background colour, which isn't really fair when you're trying to force everyone else to see what you see instead of changing your local colours.
Sometimes colours can be useful, for example, If I help somebody fix a script I use colours to highlight the changes I've made.
