Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Newtonsoft.Json;

public class Program
{
  public static void Main()
  {
    RgbaColor color = JsonConvert.DeserializeObject<RgbaColor>("{\"Hex\": 0, \"Red\": 128}");
    Console.WriteLine(color.Hex);
    Console.WriteLine(color.Red);

    color = JsonConvert.DeserializeObject<RgbaColor>("{\"Red\": 128, \"Hex\": 0}");
    Console.WriteLine(color.Hex);
    Console.WriteLine(color.Red);
  }

  private class RgbaColor 
  {
    public int Hex { get; set; }
    public byte Red
    {
      get => (byte) ((Hex & 0xff0000) >> 16);
      set
      {
        Hex = (Hex & 0x00ffff) | (((int) value) << 16);
      }
    }
  }
}