I would opt for something like this instead, to keep in the style of the others:

  runner.on(EVENT_TEST_PASS, function (test) {
    var fmt =
      indent() +
      color('checkmark', '  ' + Base.symbols.ok) +
      color('pass', ' %s');
    var fmtVars = [test.title];

    if (test.speed !== 'fast') {
      fmt += color(test.speed, ' (%dms)');
      fmtVars.push(test.duration);
    }

    if (test._currentRetry > 0) {
      fmt += color('bright yellow', ' (retry x%d)');
      fmtVars.push(test._currentRetry);
    }

    Base.consoleLog.apply(Base, [fmt].concat(fmtVars));
  });

To really stick with the theme I think we should add a 'retries' color here:

And possibly stick even more with the style of eg. durations and resolve to the color in base.js:

And maybe do a similar style and have two levels: 'some retries' / 'many retries' With only the latter resolving to bright yellow

The underscore in _currentRetry is an old-school practice for indicating that its a private property, so we shouldn't rely on it here I think as its not intended for outside consumption.

If we want it to be exposed we should make it an explicit public property, like duration, and probably name it retries or retryCount or such

We should use the public .currentRetry() instead.