Thank you for getting back to me.
RadControls for WinForms use their own theming mechanism, different from the Windows theming. There is no way to turn off our theming in order to display the Windows one.
A nice workaround in this case is to use System colors. They will be altered according to the Windows color scheme. However, this will not happen 'on the fly' - i.e. when you change the color scheme and you have a particular form opened, the color modifications will not reflect on the form's RadControls until you do something to the them - close and reopen the form or mouse hover the controls.
If you have additional questions, feel free to contact me.
All the best,
the Telerik team
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