code: function parseRGBA(rgbStr) {
    var bits = RGBA_RE.exec(rgbStr);
    if (!bits) return null;
    var r = parseInt(bits[1], 10),
        g = parseInt(bits[2], 10),
        b = parseInt(bits[3], 10);
    if (bits[4]) {
      return {r: r, g: g, b: b, a: parseFloat(bits[4])};
    } else {
      return {r: r, g: g, b: b};
    }
  }
docs: Helper for toRGB_ which parses strings of the form:
  rgb(123, 45, 67)
  rgba(123, 45, 67, 0.5)
  @return parsed {r,g,b,a?} tuple or null.