shouldTextBeDark v 1.0 Determines whether text color should be dark or not to contrast nicely with the background color, based on the visual contrast algorithm suggested by the W3C (http://www.w3.org/WAI/ER/WD-AERT/#color-contrast).

shouldTextBeDark.js

// shouldTextBeDark v 1.0
// (formerly colorContrast)

// Determines whether text color should be dark or not to
// contrast nicely with the background color.

// Based on the visual contrast algorithm suggested by the W3C
// (http://www.w3.org/WAI/ER/WD-AERT/#color-contrast)

// Call it with a RGB color:
//   e.g. shouldTextBeDark.rgb(225, 255, 255) => true
// Or with a HEX color:
//   e.g. shouldTextBeDark.hex('#FF0000')     => false

var shouldTextBeDark = new function() {

  var _hexToRgb = function(hex) {
    var channels = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
    return channels ? {
      r: parseInt(channels[1], 16),
      g: parseInt(channels[2], 16),
      b: parseInt(channels[3], 16)
    } : null;
  };

  var _calculate = function(r, g, b) {
    var contrast = ((r*299)+(g*587)+(b*114)) / 255000;
    return contrast >= 0.5 ? true : false;
  };

  this.rgb = function(r, g, b) {
    return _calculate(r, g, b);
  };

  this.hex = function(hex) {
    var rgb_a = _hexToRgb(hex);
    return _calculate(rgb_a.r, rgb_a.g, rgb_a.b);
  };

};