A design time error occurs when the control have a custom style based on the default RadColorPickerStyle. This is reproducible only if the project references NoXaml assemblies and it uses the resource dictionaries with the themes locally (the files are copied in the project and then merged in the Resources).

The error is the following:
'This feature requires service 'Microsoft.Windows.Design.Services.ValueTranslationService' to be present, but it could not be located.	'

As a workaround you can merge the resources directly from the .dll file of the theme as demonstrated in the Setting a Theme help article.
http://www.telerik.com/help/wpf/styling-apperance-implicit-styles-overview.html

Available in LIB version: 2015.1.0604