Q: How to control theme colors for Drupal 7 mass contact email
After re-reading the post I mentioned several times, I found one of the comments to actually be the answer to my problem.  That post, created by dwils03, indicated:


  In case anyone was looking for a quick and dirty fix, I just included
  a blank mail.css file in my theme's folder. The result is an
  html-formatted, NON-STYLED email.


I did the same and added an empty mail.css file in my theme folder and it solved my problem.