code: function addColorScale(name, colors, positions) {
    if (colors.length !== positions.length) {
      throw new Error('Invalid color scale.');
    }
    colorscales[name] = { colors, positions };
  }
docs: Add a new colorscale to the list of available colorscales.
  @memberof module:plotty
  @param {String} name the name of the newly defined color scale
  @param {String[]} colors the array containing the colors. Each entry shall
  adhere to the CSS color definitions.
  @param {Number[]} positions the value position for each of the colors