gistfile1.js

function Colourizer (colors) {
  this._colors = colors;
}

Colourizer.prototype.getStringColor = function (str) {
  var letters = str.split('');

  return this._colors[letters.reduce(function (n, c) {
    return n + c.charCodeAt(0)
  }, 0) % this._colors.length];
}