This brush is not exposed in RadGridView's API through a property. In order to access it at runtime, you will have to find the respective border in the visual tree an check its Background property, like illustrated in the attached project. However, I would not advise you to modify it at runtime. Would you please shed some more light on what exactly you are trying to achieve, so that we could give you some guidelines?
All the best,
Ivan Ivanov
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>