use module to strip colors AND bold/underline/reverse with chanmode +S ;)
[EDIT]
aquanight wrote:At the moment, you can't use a spamfilter to check for format codes since they are stripped from the text the regex is matched against. (IIRC).
As JanisB said... Spamfilters are not for this (nor can they see the codes), and there's a module that will strip reverse(/bold/underline/..) if the channel is +S and block it if +j.