code: function toColor(str, opacity) {
    var rgb = [0, 0, 0, opacity || 0.75];
    try {
      for (var i = 0; i < str.length; i++) {
        var v = str.charCodeAt(i);
        var idx = v % 3;
        rgb[idx] = (rgb[i % 3] + (13 * (v % 13))) % 20;
      }
    } finally {
    return 'rgba(' +
      rgb.map(function(c, idx) {
        return idx === 3 ? c : (4 + c) * 17;
      }).join(',') + ')';
    }
  }
docs: Given an arbitrary string, create a rgba color
  of a specified opacity to identify it visually.
  @param {string} str any arbitrary string
  @param {number} opacity an opacity value from 0 to 1
  @returns {string} output color
  @example
  toColor('tom') //= 'rgba(187,153,68,0.75)'
  toColor() //= 'rgba(0,0,0,0.74)'