En-flags any (sane) enum

flags.cs

void Main()
{
    Flags<Color> colors = new Flags<Color>();

    Console.WriteLine(colors);
    colors.Set(Color.Red);
    Console.WriteLine(colors);
    colors.Set(Color.White);
    Console.WriteLine(colors);
}

enum Color { Red, Black, White };

struct Flags<T>
{
    ulong value;

    private ulong Repr(T flag) => 1UL << Convert.ToInt32(flag);

    public void Set(T flag) => value |= Repr(flag);
    public void Clear(T flag) => value &= ~(Repr(flag));
    public bool Has(T flag) => (value & Repr(flag)) != 0;

    public override string ToString()
    {
        var me = this;
        return string.Join(", ", Enum.GetValues(typeof(T)).Cast<T>().Where(me.Has));
    }
}