Json type converter used as attribute on convertible class

ConcreteTypeConverter.cs

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

namespace App
{
	public class ConcreteTypeConverter<T>
		: JsonConverter
	{
		public override bool CanConvert (Type objectType)
		{
			return true;
		}

		public override object ReadJson (JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
		{
			if (objectType == typeof(Xamarin.Forms.Color))
			{
				var colorString = (string)reader.Value;
				if (colorString.StartsWith ("#"))
				{
                    if (colorString.Contains(";"))
                    {
                        var colors = colorString.Split(new char[] { ';' });
                        if (Device.OS == TargetPlatform.iOS)
                        {
                            return Xamarin.Forms.Color.FromHex(colors[0]);
                        }
                        if (Device.OS == TargetPlatform.Android)
                        {
                            return Xamarin.Forms.Color.FromHex(colors[1]);
                        }
                    }
					return Xamarin.Forms.Color.FromHex (colorString);
				}
			}
			if (objectType == typeof(List<INativeMenuItem>))
			{
				var list = serializer.Deserialize<List<NativeMenuItem>>(reader);
				var ret = new List<INativeMenuItem> ();
				foreach (var item in list)
				{
					ret.Add (new NativeMenuItem {
						Title = item.Title,
						Url = item.Url,
					});
				}
				return ret;
			}
			return serializer.Deserialize<T> (reader);
		}

		public override void WriteJson (JsonWriter writer, object value, JsonSerializer serializer)
		{
			serializer.Serialize (writer, value);
		}
	}
}

// Usage in StyleService.cs:
/*
        [JsonConverter(typeof(ConcreteTypeConverter<Xamarin.Forms.Color>))]
        public Color HeaderBarBackgroundColor { get; set; }
*/