Hello Nebras ,
Thank you for writing.
In order to achieve this you have to create a custom theme and assign it to RadMessageBox.
Here is a knowledge base article which describes this approach: Customizing RadMessageBox with custom theme
If you have any questions, do not hesitate to ask.
the Telerik team
Q1’11 SP1 of RadControls for WinForms is available for download
; also available is the Q2'11 Roadmap
for Telerik Windows Forms controls.