Hi Asem,
Thanks for using Syncfusion products.
We can change the gridlines color by using the dependency property GridLineStroke of ChartArea in the ChartAxis. The following code shows how to change the color of GridLines.
[XAML]
Similary you can set GridLines color for Secondary axis also. Based on your requirement we have created a simple sample and the same can be downloaded from the following location.
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=WPF-1485564506.zipLet me know if you have any queries
Regards ,
Muralidharan.