The solution is to rather set the node.CssClass to equal a CSS style that has the color you want.
For my requirements, I needed nodes that opened in a new browser window in green. I had client side drag and drop, as well as new node creation.
Create a style for your page
Then in your code behind, simply assign the node the style.
sender, RadTreeNodeEventArgs e)
DataRowView dbRow = (DataRowView)e.Node.DataItem;
] = dbRow[
The CCS style is retained with the node when dragging and dropping.