Ordering objects with LINQ

Ordering.cs

var apples = new[] { new Apple("Red"), new Apple("Blue"), new Apple("Green") };
var oranges = new[] { new Orange(Size.Large), new Orange(Size.Small), new Orange(Size.Medium) };

// works
Console.WriteLine(string.Join(',', apples.OrderBy(x => x)));
// throws InvalidOperationException
Console.WriteLine(string.Join(',', oranges.OrderBy(x => x)));


class Apple : IComparable<Apple>
{
    public readonly string Color;

    public Apple(string color)
    {
        Color = color;
    }

    public int CompareTo(Apple? other)
    {
        return this.Color.CompareTo(other?.Color);
    }

    public override string ToString()
    {
        return $"{Color} apple";
    }
}

class Orange
{
    public readonly Size Size;

    public Orange(Size size)
    {
        Size = size;
    }

    public override string ToString()
    {
        return $"{Size} orange";
    }
}

enum Size { Small, Medium, Large }