I think you'll find it's partly to do with being fed up with having to tell people. Generally it's bad etiquette to go using colours in a channel before properly establishing that they are allowed. IRC is so full of people who don't follow etiquette now that I just get pretty tired of having to tell people nicely every single time they break a rule.
Whoever was rude to you isn't psychic and, from what I can tell, doesn't know you from Adam? So immediately they probably just assumed you were some lamer who has no idea about IRC and couldn't be bothered with you. There are so many people like that on IRC that I kinda understand...there are so many scripts made predominantly by non-English speaking users which seem to relish in their ability to use as many colour combinations as possible, spam as much as possible, and generally be annoying.
Personally I don't see why you need to use CTRL+K to change your colours. If you want colours to appear differenly on your screen you can use ALT+K and change your 'Own text' colour.
My 2 cents (:
Regards,
