Color Contrast - http://24ways.org/2010/calculating-color-contrast/

color-contrast.js

function getContrast50(hexcolor){
  return (parseInt(hexcolor, 16) > 0xffffff/2) ? 'black':'white';
}

function getContrastYIQ(hexcolor){
  var r = parseInt(hexcolor.substr(0,2),16);
  var g = parseInt(hexcolor.substr(2,2),16);
  var b = parseInt(hexcolor.substr(4,2),16);
  var yiq = ((r*299)+(g*587)+(b*114))/1000;
  return (yiq >= 128) ? 'black' : 'white';
}