I've seen a lot of ruby weirdness over the years but this one was new to me:

1) Metric#color reps should be green when the goal is increase_is_better = true and the change is +
   Failure/Error: byebug

   LoadError:
     dlopen(/Users/sjohnson/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/x86_64-darwin16/readline.bundle, 9): Library not loaded: /usr/local/opt/readline/lib/libreadline.7.dylib
       Referenced from: /Users/sjohnson/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/x86_64-darwin16/readline.bundle
       Reason: image not found - /Users/sjohnson/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/x86_64-darwin16/readline.bundle

The solution turned out to be:

ln -s /usr/local/opt/readline/lib/libreadline.8.0.dylib /usr/local/opt/readline/lib/libreadline.7.dylib

Thank you to Zuhlfreelancer