Random CSS hexadecimal color code generator.

annotated.js

function (
  e                         // placeholder
){
  e = (
   0 |                      // shorter than a Math.floor call
   Math.random() * 16777216 // random number n, 0 <= n <= 0xFFFFFF
                            // note that 16777216 = 0xFFFFFF+1
  .toString(16);            // get the hex representation of n
  while( e.length<6 ) e=0+e;// pad with 0s if necessary

  return'#'+e
}

index.js

function(e){e=(0|Math.random()*16777216).toString(16);while(e.length<6)e=0+e;return'#'+e}

LICENSE.txt

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
                    Version 2, December 2004

 Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE>

 Everyone is permitted to copy and distribute verbatim or modified
 copies of this license document, and changing it is allowed as long
 as the name is changed.

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. You just DO WHAT THE FUCK YOU WANT TO.

package.json

{
  "name": "randomCSSHexColorCode",

  "description": "Return a random CSS hexadecimal color code.",

  "keywords": [
    "random",
    "css",
    "color"
  ]
}

Smaller function:

function(e){e=2<<23;e+=(0|Math.random()*e);return'#'+e.toString(16).slice(1)}

@atk, I bet it can be even shorter:

function(){return'#'+(1e8^Math.random()*(1<<24)).toString(16).slice(1)}

Even smaller (though potentially erroneous if Math.random ever spews out less than 6 digits after the comma - rather unlikely, but not entirely impossible):

function(){return'#'+(Math.random()).toString(16).slice(-6)}

alas, this happens sometimes. Better use:

function (){return'#'+(Math.random()*Math.PI).toString(16).slice(-6)}