Thanks for the feedback. Indeed, the BackColor property cannot be set to a string (this is what you get from the custom attribute). However, I got the impression from the code you sent earlier that you have a method which converts the string to the appropriate type for the BackColor property:
My assumption was that if I show you how to get a string value from the custom attribute you would be able to convert it to the appropriate type.
Indeed, setting the CssClass property is an alternative solution.
Feel free to contact us should you have any other questions.
the Telerik team