EditorThemeColorPicker.cs

using global::Umbraco.Core.Models.PublishedContent;
using Umbraco.Core.PropertyEditors;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Umbraco.Web;
using Umbraco.Core;
using System.Linq;

namespace YourNamespace.PropertyEditors
{
    [PropertyValueType(typeof(EditorColorTheme))]
    [PropertyValueCache(PropertyCacheValue.All, PropertyCacheLevel.Content)]
    public class EditorThemeColorPicker : PropertyValueConverterBase
    {
        public override bool IsConverter(PublishedPropertyType propertyType)
        {
            return propertyType.PropertyEditorAlias == "Our.Umbraco.EditorThemeColorPicker";
        }

        public override object ConvertDataToSource(PublishedPropertyType propertyType, object source, bool preview)
        {
            if (source == null)
            {
                return string.Empty;
            }

            return source.ToString();
        }

        public override object ConvertSourceToObject(PublishedPropertyType propertyType, object source, bool preview)
        {
            string sourceString = (string)source;

            if (sourceString.IsNullOrWhiteSpace())
            {
                return null;
            }

            var editorColorThemeData = JsonConvert.DeserializeObject<EditorColorThemeData>(sourceString);

            return new EditorColorTheme
            {
                BackgroundColor = "#" + editorColorThemeData.BackgroundColor,
                TextColor = "#" + editorColorThemeData.TextColor
            };
        }

        public class EditorColorTheme
        {
            public string BackgroundColor { get; set; }
            public string TextColor { get; set; }
        }

        public class EditorColorThemeData
        {
            public string BackgroundColor { get; set; }
            public string TextColor { get; set; }
        }

    }
}