I've read through #802 and #590

I believe I've found where the issue lies:
Snippet from base.js
https://github.com/visionmedia/mocha/blob/master/lib/reporters/base.js

exports.colors = {
    'pass': 90
  , 'fail': 31
  , 'bright pass': 92
  , 'bright fail': 91
  , 'bright yellow': 93
  , 'pending': 36
  , 'suite': 0
  , 'error title': 0
  , 'error message': 31
  , 'error stack': 90
  , 'checkmark': 32
  , 'fast': 90
  , 'medium': 33
  , 'slow': 31
  , 'green': 32
  , 'light': 90
  , 'diff gutter': 90
  , 'diff added': 42
  , 'diff removed': 41
};

var color = exports.color = function(type, str) {
  if (!exports.useColors) return str;
  return '\u001b[' + exports.colors[type] + 'm' + str + '\u001b[0m';
};

So the color function takes in a type and uses the conversion table above to get the ANSI escape color.
A chart can be found here:
http://en.wikipedia.org/wiki/ANSI_escape_code#CSI_codes

As you can see:

Seems to be a closed-source terminal from IBM AIX.
I believe nobody is using mocha on it. (Correct me if I'm wrong)

Furthermore, I found the ECMA specification:
http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-048.pdf
Here is page 62:

Color 90-99 are not in the specification. Most terminals wouldn't care implementing these colors correctly and god knows what color they'll fall back into.
And not everyone uses iTerm2, which has a contrast setting.
Please use color 30-37, if you want increased intensity then \u001b[30;1m would use the intense variant.
I think users are only responsible for configuring their terminals so the 16 colors look great on their bg/fg colors. So please don't just say "It's the theme's fault" and close the issue. It's mocha's problem not using color from the standard palette.