Coloured dialogue is one of my biggest pet peeves in this forum and the primary reason why I would skip an entire post by someone. IMO there is no good reason for it. Books don't need it. Major sites with stories don't need it. The writer and the reader should be able to tell which character is doing or saying what and to whom. If the writer needs to keep track of what's going on in their own post, thus they use colour, do it in their own word doc or on whatever they note their stories down. 

I do like when posters use the @username function to draw attention to a possible interaction.  It's like forming a thread that makes the divergent storyline easier to follow.