I truly believe that color should be disabled in forum posts because it really hinders the usability of the site. For example, links throughout the site are blue, text is dark grey, headings are purple , ... all standard throughout the site. So much effort was put into the font color, for example. (Remember the font size thread where one shade of grey made such a difference?) It really does bother me when members have the freedom to just screw up all of the effort I put in, not to mention money paid to designers who specialize in color theory. I think that my point can be proven in the fact that there are links to three different search engines in this post.
And don't go trying to tell me that the moderators should make sure things like this don't happen and that color is only used when it aids comprehension. Dave Sinkula uses blue font all the time, which is just about the one color I am the most against because it can so easily be confused with a link, especially because links on this site don't have underlines.