更改可写备份字段后,C#中的只读属性永远不会更新

我有一个非常简单的问题 Color 课程实施如下:

using System;
namespace HelloWorld
{
    internal class Color
    {
        private byte red;
        private byte green;
        private byte blue;
        private byte alpha;

        public Color(byte red, byte green, byte blue, byte alpha)
        {
            this.red = red;
            this.green = green;
            this.blue = blue;
            this.alpha = alpha;
        }

        public Color(byte red, byte green, byte blue)
        {
            this.red = red;
            this.green = green;
            this.blue = blue;
            this.alpha = 255;
        }

        public byte Red { get; set; }
        public byte Green { get; set; }
        public byte Blue { get; set; }
        public byte Alpha { get; set; }



        public float GreyScale
        {
            get
            {
                return (red + green + blue) / 3.0F;
            }
        }
    }
}

我有一个名为GreyScale的属性,它只是以浮点形式返回红色、绿色和蓝色字段的平均值。但是,当我执行下面的代码时 GreyScale 属性,对可写类成员的后续更改不会在再次调用时更改GreyScale的值。

Color color = new Color(255, 255, 255, 255);
Console.WriteLine($"{color.GreyScale}"); // prints 255 as expected
color.Red = 197;
color.Green = 197;
color.Blue = 197;
Console.WriteLine(%"{color.GreyScale}");// should print 197. Prints 255.