Hi Fabian ,
Thanks for your interest in Syncfusion products.
You can achieve your requirement by using the following code snippet and also I have attached a simple sample that demonstrates the same.
[c#]
treeViewAdv1.SelectedNode.Background = new Syncfusion.Drawing.BrushInfo(System.Drawing.Color.Pink);
[sample link]
http://www.syncfusion.com/downloads/Support/DirectTrac/97809/ChangeNodeColor-511908967.zip
Please let us know if you need any other details.
Regards,
Berkunath A