If by "controls" you are referring to other RadControls, please note that RadFormDecorator does not style them. Its purpose is to decorate standard controls like buttons, textboxes, radiobuttons, etc. More information on it can be found in our demo
If you are using RadFormDecorator but the decorated standard controls use different skin, please make sure that you haven't set the Skin property somewhere else (in the codebehind for example). If this is not the case - just open a new support ticket and send us your project so we could check it.
the Telerik team