const options = {
    [Rainbow.Red]: () => new RGBColor(0xFF, 0x00, 0x00),
    [Rainbow.Orange]: () => new RGBColor(0xFF, 0x7F, 0x00),
    [Rainbow.Yellow]: () => new RGBColor(0xFF, 0xFF, 0x00),
    [Rainbow.Green]: () => new RGBColor(0x00, 0xFF, 0x00),
    [Rainbow.Blue]: () => new RGBColor(0x00, 0x00, 0xFF),
    [Rainbow.Indigo]: () => new RGBColor(0x4B, 0x00, 0x82),
    [Rainbow.Violet]: () => new RGBColor(0x94, 0x00, 0xD3),
    default: colorBand => throw Error(`invalid enum value ${colorBand}`),
};
(options[colorBand] || options.default)(colorBand)