Are you trying to control the appearance of RadToolTip with the standard server tag properties (such as backcolor="#ff00ff")? Unfortunately, this approach will not be of much help, as the appearance of RadToolTip is controlled entirely with CSS skins. As Shinu (thanks, Shino!) has directed you, please, go through the skinning documentation of that particular control in order to get a better vision of how this should be done.
If you face difficulties, please, let us know. We will be happy to help.
All the best,
the Telerik team
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