Well, signatures are somewhat  like some kinda designs made to attract readers to clicking  their  text which is inform a url (with different colors) and if it's  in a black format, there might not be any difference  to a  normal text  .
I don't  dispute the fact of using a coloured text and for someone like you who loves a long text u might quite use it but not making it to obvious throught the text , I would  suggest  using to catch attention  towards reading  about a particular text in your construction.
Besides, there are some forum users who write long text just like you  and don't  make use of color styling,  just bold styling is beign used .