Color picker is working, added custom validation to the pre-values but need to get them working a bit better and showing the colors in the pre-val editor as well. Then also need to update the other list pre-value editors to be able to update values so we don't have to remove and re-add them.

src/Umbraco.Web/Editors/DataTypeValidateAttribute.cs

@@ -88,7 +88,7 @@ namespace Umbraco.Web.Editors
 
                 foreach (var v in propertyEditor.PreValueEditor.Fields.SelectMany(x => x.Validators))
                 {
-                    foreach (var result in v.Validate(postedValue != null ? postedValue.ToString() : null, preVal.Key, propertyEditor))
+                    foreach (var result in v.Validate(postedValue, preVal.Key, propertyEditor))
                     {
                         //if there are no member names supplied then we assume that the validation message is for the overall property
                         // not a sub field on the property editor

src/Umbraco.Web/PropertyEditors/ColorPickerPropertyEditor.cs

@@ -0,0 +1,73 @@
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using System.Text.RegularExpressions;
+using Newtonsoft.Json.Linq;
+using Umbraco.Core;
+using Umbraco.Core.PropertyEditors;
+
+namespace Umbraco.Web.PropertyEditors
+{
+    [PropertyEditor(Constants.PropertyEditors.ColorPicker, "Color Picker", "colorpicker")]
+    public class ColorPickerPropertyEditor : PropertyEditor
+    {
+        /// <summary>
+        /// Return a custom pre-value editor
+        /// </summary>
+        /// <returns></returns>
+        /// <remarks>
+        /// We are just going to re-use the ValueListPreValueEditor
+        /// </remarks>
+        protected override PreValueEditor CreatePreValueEditor()
+        {
+            return new ColorListPreValueEditor();
+        }
+
+    }
+
+    internal class ColorListPreValueEditor : ValueListPreValueEditor
+    {
+        public ColorListPreValueEditor()
+        {
+            var fields = CreatePreValueFields();
+            //change the description
+            fields.First().Description = "Add and remove colors in HEX format without a prefixed '#'";
+            //need to have some custom validation happening here
+            fields.First().Validators = new List<ValidatorBase>
+                {
+                    new ColorListValidator()
+                };
+
+            Fields = fields;
+        }
+
+        internal class ColorListValidator : ValidatorBase
+        {
+            public override IEnumerable<ValidationResult> Validate(object value, string preValues, PropertyEditor editor)
+            {
+                var json = value as JArray;
+                if (json != null)
+                {
+                    //validate each item
+                    foreach (var i in json)
+                    {
+                        //NOTE: we will be removing empty values when persisting so no need to validate
+                        var asString = i.ToString();
+                        if (asString.IsNullOrWhiteSpace() == false)
+                        {
+                            if (Regex.IsMatch(asString, "^([0-9a-f]{3}|[0-9a-f]{6})$", RegexOptions.IgnoreCase) == false)
+                            {
+                                yield return new ValidationResult("The value " + asString + " is not a valid hex color", new[]
+                                    {
+                                        //we'll make the server field name the value of the hex color so we can wire it back up to the
+                                        //individual row in the UI.
+                                        asString
+                                    });
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

src/Umbraco.Web/PropertyEditors/TextStringPropertyEditor.cs

@@ -4,11 +4,13 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Umbraco.Core;
+using Umbraco.Core.Models;
 using Umbraco.Core.PropertyEditors;
+using Umbraco.Core.Services;
 
 namespace Umbraco.Web.PropertyEditors
 {
-    [PropertyEditor(Constants.PropertyEditors.Textbox, "Textstring", "textstring")]
+    [PropertyEditor(Constants.PropertyEditors.Textbox, "Textbox", "textbox")]
     public class TextStringPropertyEditor : PropertyEditor
     {        
     }

src/Umbraco.Web/PropertyEditors/ValueListPreValueEditor.cs

@@ -91,6 +91,12 @@ namespace Umbraco.Web.PropertyEditors
                 var index = 0;
                 foreach (var item in val)
                 {
+                    var asString = item.ToString();
+                    //don't allow empties
+                    if (asString.IsNullOrWhiteSpace())
+                    {
+                        continue;
+                    }
                     result.Add(index.ToInvariantString(), item.ToString());
                     index++;
                 }

src/Umbraco.Web/Umbraco.Web.csproj

@@ -316,6 +316,7 @@
     <Compile Include="Models\Mapping\PreValueDisplayResolver.cs" />
     <Compile Include="Models\PagedResult.cs" />
     <Compile Include="PropertyEditors\CheckBoxListPropertyEditor.cs" />
+    <Compile Include="PropertyEditors\ColorPickerPropertyEditor.cs" />
     <Compile Include="PropertyEditors\DatePropertyEditor.cs" />
     <Compile Include="PropertyEditors\DateTimePropertyEditor.cs" />
     <Compile Include="PropertyEditors\DateTimeValidator.cs" />