Hi Elia,
Thanks for your interest in Syncfusion product.
If you want to change the color of LineConnector then you can use LineStyle.LineColor property of the line. Please refer to the following code snippet
LineConnector line = new LineConnector(symbol1.PinPoint, symbol2.PinPoint);
line.LineStyle.LineColor = Color.Red;
this.diagram.Model.AppendChild(line);
symbol1.CentralPort.TryConnect(line.HeadEndPoint);
symbol2.CentralPort.TryConnect(line.TailEndPoint);
Pleased refer to the attached sample
http://websamples.syncfusion.com/samples/Diagram.Windows/F66764/main.htmPlease let me know if you have any questions.
Thanks,
Nagaraj