@saul11, I would rather not use a background image because it would make printing much more complicated for color-coded text. I'm a little busy now preparing some teaching materials, but I will contact you later about doing this as a freelance project. Thanks for responding.
Re: Adding a second and a third Style menu
Can't you use an image background to mimic double or triple underlinings? Maybe increasing the bottom-padding or line-height.
Adding style dropdown should be possible, but will need custom coding...
Should you want help with this then you can contact me for freelance (FCKeditor) development at mail -a- saulmade.nl
Re: Adding a second and a third Style menu