Plays http://game.ioxapp.com/color for you

gistfile1.js

var play = function() {
  var boxes = $('#box span');
  var colors = boxes.map(function(idx, item) {
    return $(item).css('background-color');
  });
  
  var color1 = {color: $.unique(colors)[0], count: 0};
  var color2 = {color: $.unique(colors)[1], count: 0};
  
  boxes.each(function(idx, item) {
    if ($(item).css('background-color') == color1.color) {
      color1.count++;
    } else {
      color2.count++;
    }
  });
  
  if (color1.count < color2.count) {
    $('#box span[style*="' + color1.color + '"]').eq(0).click();
  } else {
    $('#box span[style*="' + color2.color + '"]').eq(0).click();
  }
  
  setTimeout(play, 1);
}

Minor speed improvement:

$('#box').css('display', 'none');
var play = function() {
  var boxes = $('#box span'), 
      color1 = {count: 0},
      color2 = {count: 0},
      lastColor1Item, lastColor2Item;

  boxes.each(function(idx, item) {
    var color = $(item).css('background-color');
    if (!color1.color) {
      color1.color = color;
    }
    if (color == color1.color) {
      color1.count++;
      lastColor1Item = item;
    } else {
      if (!color2.color) {
          color2.color = color;
      }
      color2.count++;
      lastColor2Item = item;
    }
  });

  if (color1.count < color2.count) {
    $(lastColor1Item).click();
  } else {
    $(lastColor2Item).click();
  }

  setTimeout(play, 0);
}

Breaking the each loop in the right moment improves even more with:

if (color1.color && color2.color && (color1.count > 1 || color2.count > 1)) {
  return false;
}