You can apply a custom theme to any of the controls. For more information you can follow the link below:
Please find the following attached files:
In the attached image file I marked with Red color which Brushes you have to Edit.
In the second attached file is a project with a custom style of the RadRadioButton control.
If you have further questions please do not hesitate to ask us.
I hope this will help you.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items.