title_body: Maintain font color when changing background color in ebook
upvoted_answer: Amazon may have resolved this for us, or it's just one of those things that worked itself out. I haven't changed the CSS at all after posting the question, but I DID convert the book to KFX format using the plugin for Calibre, and the renamed the KFX file with a .mobi extension, opened it in Kindle for Mac, and viola the colors are sticking:  
  
  What you're seeing here is red font displayed in "night mode" - so I don't know if it's a factor of the "basic" mobi format (which would have changed this to white text) versus the KFX format (which is what Amazon delivers to a buyer through the Kindle store), but I would presume that this would be preserved through the KDP publishing process. Never a guarantee though.
  
  PS sorry, I don't have time tonight to post how I went through the above process, but I can if someone needs it and leaves a comment.