hex2rgb.js

// cache from global scope
var _parseInt = this.parseInt;

_speedTest(
  [
    function(n)
    {
      var r, g, b, s = '#aabbcc';
      var i = n; while(i--)
      {
        var h = _parseInt(s.slice(1), 16);

        r = (h >>> 16) /* & 0xff */;
        g = (h >>> 8) & 0xff;
        b = (h     ) & 0xff;
      }    
    },
    function(n)
    {
      var r, g, b, s = '#aabbcc';
      var i = n; while(i--)
      {
        var h = +('0x' + s.slice(1));

        r = (h >>> 16) /* & 0xff */;
        g = (h >>> 8) & 0xff;
        b = (h     ) & 0xff;
      }    
    },
    function(n)
    {
      var r, g, b, s = '#aabbcc';
      var i = n; while(i--)
      {
        r = _parseInt(s.substr(1, 2), 16);
        g = _parseInt(s.substr(3, 2), 16);
        b = _parseInt(s.substr(5, 2), 16);
      }    
    }
  ],
  1000000
);

/*
chrome5 1000000
0: 782 ms
1: 999 ms
2: 2143 ms

opera 10.60 1000000
0: 2041 ms
1: 2499 ms
2: 4674 ms

ie7 1000000/10
0: 1171 ms
1: 1002 ms
2: 3034 ms

ff3.6 1000000
0: 1985 ms
1: 2907 ms
2: 4945 ms
*/

What about shorthand hex format, as in #FFF?

@GarrettS by analogy
var h = parseInt(s.slice(1), 16);
var r = 0x11((h >>> 8) );
var g = 0x11_((h >>> 4) & 0xf);
var b = 0x11*((h ) & 0xf);