Telerik does not support the Web site Management 10.1 (RedDot) application and my recommendation is to ask the developers of RedDot how to configure RadEditor in it.
Just for any case you can see the following articles which could be helpful: Skin Basics
If you use RadEditor Classic (bin/RadEditor.dll, which is not supported since 2009) see this article:
If you use RadEditor for ASP.NET AJAX (bin/Telerik.Web.UI.dll) check this one: Skins
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